#Denmark - #Influenza A #H5N5 viruses of high pathogenicity (Inf. with) (non-poultry including wild birds) (2017-) - Immediate notification

 

{A black headed gull. By © Hans Hillewaert, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=5548312}

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According to article 10.4.1.4 of the Terrestrial Animal Health Code, Member Countries should not impose bans on the trade in poultry commodities in response to notification on the presence of any influenza A virus in birds other than poultry

A wild black-headed gull.

Source: 

Link: https://wahis.woah.org/#/in-review/7385

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Recommended #composition of #influenza virus #vaccines for use in the 2026 – 2027 northern hemisphere influenza season (#WHO, Feb. 27 '26)

 

February 2026 

WHO convenes technical consultations {1} in February and September each year to recommend viruses for inclusion in influenza vaccines {2} for the northern hemisphere (NH) and southern hemisphere (SH) influenza seasons, respectively. 

This recommendation relates to the influenza vaccines for use in the NH 2026-2027 influenza season. 

A recommendation will be made in September 2026 relating to vaccines that will be used for the SH 2027 influenza season. 

WHO guidance for choosing between the NH and SH formulations for countries in tropical and subtropical regions is available on the WHO Global Influenza Programme website {3}.  

National or regional authorities approve the composition and formulation of influenza vaccines used in each country. 

National public health authorities are responsible for making recommendations regarding the use of the vaccine. 

WHO has published recommendations on the prevention of influenza {4}.  

Seasonal influenza activity 

From September 2025 through January 2026, influenza activity was reported in all transmission zones. 

Overall influenza virus detections were higher compared to the same reporting period in 2024-2025 but peaked in December 2025 for this recent period compared to February 2025 for the previous period. 

During this reporting period, influenza A viruses predominated, although the proportion of virus detections varied among transmission zones. 

In Africa, influenza activity increased during the start of the reporting period, with a predominance of influenza A viruses in all transmission zones. 

In Eastern, Northern, and Western Africa, among subtyped influenza A viruses, A(H1N1)pdm09 viruses accounted for the majority of detections early in the reporting period while A(H3N2) viruses predominated later in the reporting period. 

Influenza detections peaked in November in Western Africa and December in Eastern and Northern Africa. 

In Middle Africa, influenza detections remained low throughout the reporting period with a slight predominance of A(H1N1)pdm09 viruses early in the reporting period. 

In Southern Africa, influenza detections remained low throughout the reporting period, with a predominance of influenza A viruses. 

In Northern and Middle Africa, there was low and sustained influenza B activity throughout the reporting period. 

In Asia, influenza activity increased during the start of the reporting period in South East and Western Asia, from October in Central and Eastern Asia, and from November in Southern Asia, with a predominance of influenza A viruses in all transmission zones. 

Most influenza detections were reported from Eastern Asia, where activity peaked in early December. 

In Southern Asia, influenza activity also peaked in December; in Central Asia influenza activity peaked in November, and in Western and South East Asia, influenza activity peaked in October. 

Among subtyped influenza A viruses, A(H3N2) viruses accounted for the majority of detections in all transmission zones; detections of A(H1N1)pdm09 and influenza B viruses remained low in most transmission zones throughout the reporting period, except in Eastern Asia where there was a substantial rise in influenza B viruses in recent weeks. 

In Europe, influenza activity increased from mid-September in Northern Europe, from October in South West Europe and from mid-November in Eastern Europe, with a predominance of influenza A viruses in all transmission zones. 

Influenza detections peaked in December in Northern and South West Europe but remained elevated through January. 

Influenza detections continued to increase through January in Eastern Europe. 

Among subtyped influenza A viruses, A(H3N2) viruses predominated. 

In South West Europe, detections of A(H1N1)pdm09 viruses slightly increased in mid-November. 

In Eastern and Northern Europe, detections of A(H1N1)pdm09 and influenza B viruses remained low throughout the reporting period.  

In the Americas, influenza activity increased from the start of the reporting period in Temperate and Tropical South America and from November in North America and Central America Caribbean. 

Influenza A viruses accounted for most detections, and influenza B virus detections remained low throughout the reporting period in all transmission zones, except in North America where there was a substantial rise in influenza B viruses in recent weeks. 

In North America, activity peaked in late December. 

Among subtyped influenza A viruses, there was a predominance of A(H3N2) viruses. 

In Central America Caribbean, influenza activity remained elevated through mid-January with A(H3N2) virus detections predominant from December. 

In Tropical South America, influenza activity peaked in early November and slowly declined until the end of the reporting period. 

Among subtyped influenza A viruses, A(H3N2) predominated through November then co-circulated at similar proportions to A(H1N1)pdm09 until the end of the reporting period. 

In Temperate South America, influenza activity peaked in mid-November and among subtyped influenza A viruses, A(H3N2) viruses predominated throughout the reporting period.  

In Oceania, influenza activity decreased until mid-October, increased in December and decreased since mid-December. A(H1N1)pdm09 and B viruses were detected at similar levels until mid-September and A(H3N2) virus detections predominated since then. 

Influenza A 

Globally, influenza A virus detections greatly outnumbered those of influenza B. 

Among subtyped influenza A viruses, A(H3N2) viruses predominated throughout the reporting period in most transmission zones. 

In Eastern, Northern, Western Africa, Central America Caribbean and Oceania, influenza A(H1N1)pdm09 virus detections predominated during the first part of the reporting period, and A(H3N2) virus detections predominated in the latter part of the reporting period. 

Influenza A(H1N1)pdm09 virus detections increased slightly towards the latter part of the reporting period in Eastern and South West Europe, Central America Caribbean and Tropical South America. 

The overall number of influenza detections was low in Middle and Southern Africa. 

Influenza B 

Globally, influenza B virus detections remained low throughout the reporting period. 

Increases in influenza B virus detections in January were reported in North America and Eastern Asia. 

All influenza B viruses where lineage was confirmed belonged to the B/Victoria lineage. 

(...)

Zoonotic influenza  

From 23 September 2025, sporadic zoonotic influenza infections were reported, in most cases, following exposure to infected birds, swine or contaminated environments. 

Single cases of A(H5N1) from Bangladesh, A(H5N2) from Mexico, and A(H5N5) from the United States of America were reported. 

Three A(H5N1) cases were reported from Cambodia. 

Fourteen cases of A(H9N2) and one case of A(H10N3) were reported from China. 

Single cases of A(H1N1)v and A(H1N2)v were reported from China, a case of A(H1N2)v from the United States of America, and a case of A(H3N2)v from Brazil. 

Genetic and antigenic characteristics of recent seasonal influenza viruses, human serology and antiviral susceptibility 

Influenza A(H1N1)pdm09 viruses  

Since September 2025, A(H1N1)pdm09 viruses circulated globally, but did not predominate in any region. 

The haemagglutinin (HA) genes of viruses that were genetically characterized belonged to the 5a.2a and 5a.2a.1 clades. 

Viruses from clade 5a.2a subclades C.1, C.1.9 and C.1.9.3 circulated in low numbers, with the largest proportion of detections in Africa {5}. 

Since September 2025, clade 5a.2a.1 subclades D.3.1 and D.3.1.1 viruses circulated globally. 

The D.3.1 subclade with substitutions T120A, I372V, I460T and V520A predominated in Western Pacific, Africa, South East Asia and several countries in the Americas. 

D.3.1.1 viruses characterized by R113K and more recently acquired substitutions A139D, E283K and K302E predominated in some countries in Europe, the Middle East and North America. 

The antigenic properties of A(H1N1)pdm09 viruses were assessed in haemagglutination inhibition (HI) assays with post-infection ferret antisera. 

HI results for viruses with collection dates since September 2025 showed that ferret antisera raised against cell culture-propagated A/Wisconsin/67/2022-like and eggpropagated A/Victoria/4897/2022-like viruses from the 5a.2a.1 clade recognized viruses in both 5a.2a and 5a.2a.1 clades well. 

However, post-infection ferret antisera raised against viruses from clade 5a.2a showed some reduction in recognition of the now predominating D.3.1 and D.3.1.1 subclade viruses. 

Post-infection ferret antisera raised against viruses from subclade D.3.1 (e.g., A/Missouri/11/2025) recognized recently circulating viruses from both 5a.2a and 5a.2a.1 clades well.  

Human serology studies used 15 serum panels from children, adults (18 to 64 years) and older adults (≥65 years) who had received egg-propagated inactivated (standard, high dose or adjuvanted), cell culture-propagated inactivated or recombinant trivalent or quadrivalent vaccines with NH 2025-2026 influenza vaccine formulations. 

-- NH 2025-2026 egg-based vaccines contained A/Victoria/4897/2022 (H1N1)pdm09like, 

-- A/Croatia/10136RV/2023 (H3N2)-like, 

-- B/Austria/1359417/2021-like (B/Victoria lineage) and, in quadrivalent vaccines, 

-- B/Phuket/3073/2013-like (B/Yamagata lineage) virus antigens. 

Cell culture-propagated and recombinant vaccines contained A/Wisconsin/67/2022 (H1N1)pdm09-like, A/District of Columbia/27/2023 (H3N2)-like and B/Austria/1359417/2021-like (B/Victoria lineage) virus antigens. 

Recent A(H1N1)pdm09 viruses with HA genes from clades 5a.2a (subclade C.1.9.3) and 5a.2a.1 (subclades D.3.1 and D.3.1.1) were analysed in HI assays using these human serum panels. 

When compared to the responses to cell culture-propagated A/Wisconsin/67/2022 (H1N1)pdm09-like vaccine reference viruses, post-vaccination geometric mean titres (GMTs) were significantly reduced for some recently circulating viruses from D.3.1 and D.3.1.1 subclades. 

Of 1 161 A(H1N1)pdm09 virus clinical samples and isolates examined by genetic and/or phenotypic analyses, 15 viruses showed evidence of reduced susceptibility to neuraminidase inhibitors (NAIs): seven had an H275Y neuraminidase (NA) substitution and eight had I223V and S247N substitutions. 

Of 1 331 A(H1N1)pdm09 viruses examined by genetic and/or phenotypic analyses, no viruses showed evidence of reduced susceptibility to the endonuclease inhibitor baloxavir marboxil. 

Influenza A(H3N2) viruses  

Phylogenetic analysis of the HA gene sequences of A(H3N2) viruses collected since September 2025 showed that the vast majority of viruses belonged to one of the J.2 subclades {6}, expressing HA N122D and K276E substitutions. 

HA genes have diversified with many subclades; J.2.2 (characterized by S124N), J.2.3 (characterized by N158K, K189R and S378N), J.2.4 (characterized by T135K [a potential loss of an N-glycosylation site] and K189R), and K (formerly designated as J.2.4.1; characterized by K2N, S144N [a potential addition of an N-glycosylation site], N158D, I160K, Q173R, T328A and S378N). 

During this reporting period, subclade K viruses were detected in all regions and predominated in many countries. 

There was still circulation of other J.2 subclades, notably J.2 or J.2.3 in South America, J.2.2 or J.2.4 in Africa and Asia.  

Post-infection ferret antisera raised against cell culture-propagated A/District of Columbia/27/2023-like and egg-propagated A/Croatia/10136RV/2023-like (clade 2a.3a.1, subclade J.2) viruses, representing the A(H3N2) component for the NH 2025-2026 influenza vaccines, showed poor recognition with recently circulating subclade J.2.3 (e.g., A/Netherlands/10685/2024), J.2.4 (e.g., A/Sydney/1359/2024) and K (e.g., A/Darwin/1415/2025) viruses. 

Ferret antisera raised against reference viruses from J.2.3 subclades showed good recognition of viruses expressing HA from J.2.3, but poor recognition of other subclades.  

Post-infection ferret antisera raised against cell culture-propagated A/Sydney/1359/2024-like and eggpropagated A/Singapore/GP20238/2024-like J.2.4 viruses, representing SH 2026 influenza vaccines, recognized most J.2.4 viruses and many subclade K viruses well. 

However, subclade K viruses and J.2.4 viruses with HA substitutions F79V, S144N (addition of a potential N-glycosylation site), N158D, I160K, T328A were better recognized by post-infection ferret antisera raised against cell culture-propagated A/Darwin/1415/2025-like and egg-propagated A/Darwin/1454/2025-like (subclade K) viruses. 

Human serology studies were conducted using the serum panels as described above by HI and virus neutralization (VN) assays with recent circulating A(H3N2) viruses with HA genes from subclades J.2, J.2.2, J.2.3, J.2.4, J.2.5 and K. 

When compared to titres against cell-propagated A/District of Columbia/27/2023-like vaccine reference viruses, post-vaccination HI GMTs or VN GMTs against many of the recent viruses in all subclades tested were significantly reduced in many serum panels.  

(...)

Of 4 458 influenza A(H3N2) viruses examined by genetic and/or phenotypic analyses, two viruses showed evidence of reduced susceptibility to NAIs; both had an NA E119V substitution. 

Of 4 828 A(H3N2) viruses examined by genetic and/or phenotypic analyses, nine viruses showed evidence of reduced susceptibility to the endonuclease inhibitor baloxavir marboxil: three had a PA I38T substitution, three had a PA I38I/T substitution, two had a PA I38I/M substitution and one had a PA E199E/G substitution.  

Influenza B viruses  

Since September 2025, influenza B viruses were detected in all WHO regions, and all those characterized belonged to the B/Victoria lineage. 

There have been no confirmed detections of circulating B/Yamagata lineage viruses after March 2020.  

All HA genes of B/Victoria lineage viruses characterized during this reporting period belonged to clade 3a.2 with HA substitutions A127T, P144L, and K203R. 

Viruses with clade 3a.2 HA genes have diversified further, forming several subclades (C.1-C.5)7. 

Viruses designated as C.5, C.5.1, C.5.6, C.5.6.1 and C.5.7, all of which had the HA substitution D197E, circulated at varying proportions in different regions. 

Viruses designated as C.3 have HA substitutions E128K, A154E and S208P. 

Subclade C.3.1 viruses shared additional mutations D197N (addition of a potential N-glycosylation site) and P208S. 

Recent C.3 viruses which had additional changes D197N (addition of a potential N-glycosylation site), S255P and I267V and C.3.1 viruses have been detected in increasing proportions in Eastern Asia and North America in recent weeks. 

Antigenic analysis showed that post-infection ferret antisera raised against B/Austria/1359417/2021-like viruses (3a.2), representing the vaccine viruses for the SH 2026 and NH 2025-2026 influenza seasons, recognized viruses within the C.5.1, C.5.6, C.5.6.1 and C.5.7 subclades well. 

C.3 and C.3.1 subclade viruses with the HA substitution D197N were recognized poorly. 

Post-infection ferret antisera raised against cell culture-propagated viruses from subclade C.3.1 (e.g., B/Pennsylvania/14/2025) recognized recently circulating viruses from C.3, C.3.1 and other 3a.2 subclades well. 

All available egg isolates for subclade C.3 and C.3.1 viruses acquired substitutions that remove the potential N-glycosylation site at HA 197 to 199. 

Post-infection ferret antisera raised against egg-propagated viruses from subclade C.3.1 (e.g., B/Tokyo/EIS13-175/2025, B/Tokyo/EIS13-011/2025, B/Perth/115/2025) showed reduced recognition of recently circulating viruses from C.3 and C.3.1 subclades compared to that of the cell equivalent.  

(...)

In human serology studies, recently circulating B/Victoria lineage viruses with HA genes from clade 3a.2 subclades C.3, C.3.1, C.5.1, C.5.6, C.5.6.1 and C.5.7 were tested using the serum panels described above. 

When compared to titres against egg- or cell culture-propagated B/Austria/1359417/2021-like vaccine reference virus, titres against most viruses with HA genes from C.5.1, C.5.6, C.5.6.1 and C.5.7 subclades were not significantly reduced; however, titres against viruses with HA genes from C.3 and C.3.1 were significantly reduced in most serum panels. Serology studies were not performed for B/Yamagata lineage viruses.  

Of 549 influenza B/Victoria lineage viruses examined by genetic and/or phenotypic analyses, two showed evidence of reduced or highly reduced susceptibility to NAIs, both with an NA M464T substitution. 

Of 760 B/Victoria lineage viruses examined by genetic and/or phenotypic analyses, no viruses showed evidence of reduced susceptibility to the endonuclease inhibitor baloxavir marboxil.  

Recommended composition of influenza virus vaccines for use in the 2026-2027 northern hemisphere influenza season  

Since September 2025, A(H1N1)pdm09 viruses circulated globally. The majority of viruses had HA genes belonging to the 5a.2a.1 clade which has further diversified into the D.3.1 and D.3.1.1 subclades. 

Postinfection ferret antisera raised against the northern hemisphere (NH) 2025-2026 A(H1N1)pdm09 vaccine viruses (cell culture-propagated A/Wisconsin/67/2022 and egg-propagated A/Victoria/4897/2022) and the southern hemisphere (SH) 2026 A(H1N1)pdm09 vaccine viruses A/Missouri/11/2025 recognized D.3.1 and D.3.1.1 viruses well. 

In human serology studies, post-vaccination geometric mean titres (GMTs) were significantly reduced for some recently circulating A(H1N1)pdm09 viruses when compared to the responses to cell culture-propagated A/Wisconsin/67/2022 A(H1N1)pdm09-like vaccine reference viruses. 

Since September 2025, A(H3N2) viruses circulated and predominated globally. 

The vast majority of A(H3N2) viruses collected had HA genes from subclades of J.2 and have continued to diversify with subclade K (previously designated as J.2.4.1) viruses predominating in most regions. 

Post-infection ferret antisera raised against NH 2025-2026 influenza season vaccine viruses (cell culture-propagated A/District of Columbia/27/2023 and egg-propagated A/Croatia/10136RV/2023) recognized some J.2 viruses well but showed poor recognition of viruses from subclades J.2.3, J.2.4 and K. 

Post-infection ferret antisera raised against subclade K viruses (cell culture-propagated A/Darwin/1415/2025 and egg-propagated A/Darwin/1454/2025) showed improved recognition of K viruses compared to post-infection antisera raised against NH 2025-2026 and SH 2026 A(H3N2) vaccine viruses. 

When compared to titres against cell culture-propagated A/District of Columbia/27/2023-like vaccine reference viruses, human post-vaccination haemagglutinin inhibition (HI) GMTs or virus neutralisation (VN) GMTs against many of the recent viruses in J.2.3, J.2.4 and K subclades were significantly reduced. 

Since September 2025, influenza B virus detections remained low globally, although some countries had increased detections in recent weeks. All circulating influenza B viruses characterized belonged to the B/Victoria lineage, and had HA genes belonging to clade 3a.2 with substitutions A127T, P144L and K203R. 

Post-infection ferret antisera raised against B/Austria/1359417/2021-like viruses (3a.2), representing the vaccine viruses for the SH 2026 and NH 2025-2026 influenza seasons, recognized viruses within the C.5.1, C.5.6, C.5.6.1 and C.5.7 subclades well. C.3 and C.3.1 subclade viruses with HA substitution D197N were recognized poorly. 

Post-infection ferret antisera raised against cell culture-propagated viruses from subclade C.3.1 (e.g., B/Pennsylvania/14/2025) recognized recently circulating viruses from C.3, C.3.1 and other 3a.2 subclades well. All available egg isolates for subclade C.3 and C.3.1 viruses (e.g., B/Tokyo/EIS13-175/2025) acquired egg-adaptive mutations that remove the potential N-glycosylation site at HA 197 to 199, leading to post-infection ferret antisera raised against egg-propagated viruses from subclade C.3.1 (e.g., B/Tokyo/EIS13-175/2025) showing reduced recognition of recently circulating viruses from C.3 and C.3.1 subclades compared to that of the cell equivalent. 

Human serology assays showed that post-vaccination titres against most recent B/Victoria lineage viruses with HA genes from subclades C.5.1, C.5.6, C.5.6.1 and C.5.7 were not significantly reduced when compared to titres against egg- or cell culturepropagated B/Austria/1359417/2021-like vaccine reference viruses. Titres against viruses with HA genes from subclade C.3 and C.3.1 were significantly reduced in most serum panels.  

For vaccines for use in the 2026-2027 northern hemisphere influenza season, WHO recommends the following:  

Egg-based vaccines  

• an A/Missouri/11/2025 (H1N1)pdm09-like virus;  

• an A/Darwin/1454/2025 (H3N2)-like virus; and  

• a B/Tokyo/EIS13-175/2025 (B/Victoria lineage)-like virus.  

Cell culture-, recombinant protein- or nucleic acid-based vaccines  

• an A/Missouri/11/2025 (H1N1)pdm09-like virus;  

• an A/Darwin/1415/2025 (H3N2)-like virus; and  

• a B/Pennsylvania/14/2025 (B/Victoria lineage)-like virus.  

Lists of prototype viruses for egg-, cell culture-, recombinant protein- and nucleic acid-based vaccines together with candidate vaccine viruses (CVVs) suitable for the development and production of human influenza vaccines are available on the WHO website {8}. 

A list of reagents for vaccine standardization, including those for this recommendation, can also be found on the WHO website.  

CVVs and reagents for use in the laboratory standardization of inactivated vaccines may be obtained from:  

• Therapeutic Goods Administration, P.O. Box 100, Woden, ACT, 2606, Australia (email: influenza.reagents@health.gov.au; website: http://www.tga.gov.au).  

• Medicines and Healthcare products Regulatory Agency (MHRA), Blanche Lane, South Mimms, Potters Bar, Hertfordshire, EN6 3QG, the United Kingdom of Great Britain and Northern Ireland  • (email: enquiries@mhra.gov.uk; website: http://www.nibsc.org/science_and_research/virology/influenza_resource_.aspx). 

• Division of Biological Standards and Quality Control, Center for Biologics Evaluation and Research, Food and Drug Administration, 10903 New Hampshire Avenue, Silver Spring, Maryland, 20993, the United States of America (email: cbershippingrequests@fda.hhs.gov).  

• Research Centre for Influenza and Respiratory Viruses, National Institute of Infectious Diseases, 4-7-1 Gakuen, Musashi-Murayama, Tokyo 208-0011, Japan (email: flu-vaccine@nih.go.jp).  

Requests for reference viruses should be addressed to:  

• WHO Collaborating Centre for Reference and Research on Influenza, VIDRL, Peter Doherty Institute, 792 Elizabeth Street, Melbourne, Victoria 3000, Australia (email: whoflu@influenzacentre.org; website: http://www.influenzacentre.org).  

• WHO Collaborating Centre for Reference and Research on Influenza, National Institute of Infectious Diseases, Japan Institute for Health Security 4-7-1 Gakuen, Musashi-Murayama, Tokyo 208-0011, Japan (email: whocc-flu@nih.go.jp).  

• Influenza Division, Centers for Disease Control and Prevention, 1600 Clifton Road, Mail Stop H17-5, Atlanta, GA 30329, the United States of America (email: InfluenzaVirusSurvei@cdc.gov; website: http://www.cdc.gov/flu/).  

- WHO Collaborating Centre for Reference and Research on Influenza, The Francis Crick Institute, 1 Midland Road, London NW1 1AT, the United Kingdom of Great Britain and Northern Ireland (Tel: +44 203 796 1520 or +44 203 796 2444, email: whocc@crick.ac.uk;  • website: http://www.crick.ac.uk/research/worldwideinfluenza-centre).  

• WHO Collaborating Centre for Reference and Research on Influenza, National Institute for Viral Disease Control and Prevention, China CDC, 155 Changbai Road, Changping District, 102206, Beijing, China. (tel: +86 10 5890 0851; email: fluchina@ivdc.chinacdc.cn; website: https://ivdc.chinacdc.cn/cnic/en/).  

WHO provides weekly updates {9} of global influenza activity. Other information about influenza surveillance, risk assessment, preparedness and response can be found on the WHO Global Influenza Programme website {10}.  

Acknowledgements  

The WHO recommendation on vaccine composition is based on the year-round work of the WHO Global Influenza Surveillance and Response System (GISRS). We thank the National Influenza Centres (NICs) of GISRS, and non-GISRS laboratories including the World Organization for Animal Health (WOAH) and the Food and Agriculture Organization of the United Nations (FAO) Network of Expertise on Animal Influenza (OFFLU), who contributed information, clinical specimens, viruses and associated data; WHO Collaborating Centres of GISRS for their in-depth characterization and comprehensive analysis of viruses; University of Cambridge for performing antigenic cartography and phylogenetic analysis; WHO Essential Regulatory Laboratories of GISRS for their complementary virus analyses and contributions from a regulatory perspective; and laboratories involved in the production of high growth/yield reassortants as candidate vaccine viruses. We also acknowledge the GISAID Global Data Science Initiative for the EpiFluTM database and other sequence databases which were used to share gene sequences and associated information; modelling groups for virus fitness forecasting; and the Global Influenza Vaccine Effectiveness (GIVE) Collaboration for sharing estimates of influenza vaccine effectiveness on a confidential basis.  

(...)

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{1} Recommendations for influenza vaccine composition: https://www.who.int/teams/global-influenza-programme/vaccines/who-recommendations 

{2} Description of the process of influenza vaccine virus selection and development: http://www.who.int/gb/pip/pdf_files/Fluvaccvirusselection.pdf 

{3} Vaccines in tropics and subtropics: https://www.who.int/teams/global-influenza-programme/vaccines/vaccine-in-tropics-and-subtropics 

{4} Vaccines against influenza WHO position paper – May 2022. Wkly Epidemiol Rec 2022; 97 (19): 185 - 208. Available at: https://iris.who.int/handle/10665/354264 

{5} Real-time tracking of influenza A(H1N1)pdm09 evolution: https://nextstrain.org/seasonal-flu/h1n1pdm/ha/2y?c=subclade 

{6} Real-time tracking of influenza A(H3N2) evolution: https://nextstrain.org/seasonal-flu/h3n2/ha/2y?c=subclade 

{7} Real-time tracking of influenza B/Victoria lineage evolution: https://nextstrain.org/seasonal-flu/vic/ha/2y?c=subclade 

{8} Candidate vaccine viruses: https://www.who.int/teams/global-influenza-programme/vaccines/who-recommendations/candidate-vaccine-viruses 

{9} Current respiratory virus update: https://www.who.int/teams/global-influenza-programme/surveillance-and-monitoring/influenza-updates 

{10} Global Influenza Programme: https://www.who.int/teams/global-influenza-programme 

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Source: 

Link: https://www.who.int/publications/m/item/recommended-composition-of-influenza-virus-vaccines-for-use-in-the-2026-2027-northern-hemisphere-influenza-season

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Multiple Introductions of Highly Pathogenic Avian #Influenza Viruses into the High #Arctic: #Svalbard and Jan Mayen, 2022 - 2025

 

Abstract

Between 2022 and 2025, highly pathogenic avian influenza viruses (HPAIVs) of clade 2.3.4.4b, including four distinct H5 Eurasian (EA) genotypes, were detected in wild birds and mammals in the Svalbard Archipelago and on the island of Jan Mayen. We describe their epidemiology and genomic characteristics to improve understanding of HPAIV occurrence and transmission in the High Arctic. The initial cases in 2022 occurred during summer and involved a glaucous gull (Larus hyperboreus) and great skuas (Stercorarius skua) on Svalbard and Jan Mayen, representing the first detections of HPAIVs in the High Arctic. Three HPAIV genotypes were identified: EA-2020-C (H5N1), EA-2021-AB (H5N1), and EA-2021-I (H5N5). In 2023, HPAIVs were detected in a broader range of bird species, and retrospectively in an Atlantic walrus reported by another research group (Odobenus rosmarus rosmarus). Genotypes identified in 2023 were EA-2020-C (H5N1), EA-2021-I (H5N5), and EA-2022-BB (H5N1). No cases were reported in 2024. In 2025, EA-2021-I (H5N5) was detected in Arctic foxes (Vulpes lagopus) on Svalbard, without preceding detections in wild birds. The foxes exhibited neurological symptoms, and necropsy of one individual revealed the presence of feathers in its stomach. All sequenced viruses from the Arctic foxes uniquely carried the combination of PB2-E627K and PB1-H115Q, which is associated with mammalian adaptation. The detection of multiple genotypes indicates repeated and independent introductions of HPAIVs into these regions. The co-circulation of genetically distinct virus strains in areas of high bird density further suggests that Arctic breeding grounds may facilitate local viral amplification, reassortment, and subsequent dissemination along migratory flyways, including transcontinental spread.

Competing Interest Statement

The authors have declared no competing interest.

Funder Information Declared

EU4Health, 101132473

The Research Council of Norway, https://ror.org/00epmv149, 352880

The SEAPOP program, 192141

Source: 

Link: https://www.biorxiv.org/content/10.64898/2026.02.17.706283v1

____

#Influenza at the #human - #animal #interface - Summary and #risk #assessment, from 6 November to 19 December 2025 (#WHO, edited)

 

Influenza at the human-animal interface 

Summary and risk assessment, from 6 November to 19 December 2025 {1}

-- New human cases {1,2}: 

- From 6 November to 19 December 2025, based on reporting date, the detection of influenza A(H5N1) in one human, A(H5N5) in one human, A(H9N2) in seven humans, and an influenza A(H1N1) variant virus in one human were reported officially. 

- In addition, one human case of infection with an influenza A(H1N2) variant virus was detected. 

-- Circulation of influenza viruses with zoonotic potential in animals: 

- High pathogenicity avian influenza (HPAI) events in poultry and non-poultry animal species continue to be reported to the World Organisation for Animal Health (WOAH).{3} 

- The Food and Agriculture Organization of the United Nations (FAO) also provides a global update on avian influenza viruses with pandemic potential.{4} 

- Additionally, low pathogenicity avian influenza viruses as well as swine influenza viruses continue to circulate in animal populations. 

-- Risk assessment {5}: 

- Sustained human to human transmission has not been reported associated with the above-mentioned human infection events. 

- Based on information available at the time of this risk assessment update, the overall public health risk from currently known influenza A viruses detected at the human-animal interface has not changed and remains low. 

- The occurrence of sustained human-to-human transmission of these viruses is currently considered unlikely. 

- Although human infections with viruses of animal origin are infrequent, they are not unexpected at the human-animal interface.  

-- IHR compliance {6}: 

- This includes any influenza A virus that has demonstrated the capacity to infect a human and its haemagglutinin (HA) gene (or protein) is not a mutated form of those, i.e. A(H1) or A(H3), circulating widely in the human population. 

- Information from these notifications is critical to inform risk assessments for influenza at the human-animal interface.  

Avian influenza viruses in humans 

-- Current situation:  

- Since the last risk assessment of 5 November 2025, one laboratory-confirmed human case of A(H5N1) infection was detected in Cambodia, and one laboratory-confirmed human case of A(H5N5) virus infection was detected in the United States of America. 

A(H5N1), Cambodia 

- On 16 November 2025, Cambodia notified WHO of a confirmed human infection with avian influenza A(H5N1) in a 22-year-old male from Phnom Penh. 

- The case developed symptoms on 10 November 2025, sought medical care at a clinic, and was diagnosed with pneumonia. 

- He was subsequently admitted to the national hospital in Phnom Penh on 13 November. 

- Samples were collected on the same day and tested positive for avian influenza A(H5N1) on 15 November. 

- His condition deteriorated rapidly, and he died the same day.   

- Investigations conducted in the case's hometown in Kampong Cham Province, which he visited between 4 and 6 November, revealed that the case had apparently healthy domestic birds (chickens and ducks) in his house. 

- However, sick and dead poultry had been reported in the village since 15 October. 

- Samples collected from two ducks and one chicken in the village tested positive for influenza A(H5N1). 

- Enhanced public health surveillance was implemented. 

- Among the case’s contacts, one was symptomatic, and all contacts tested negative for influenza A(H5N1).  

- Eighteen human infections with A(H5N1) viruses have been confirmed in Cambodia in 2025 and nine of these have been fatal. 

- All these cases in 2025 had exposure to domestic birds or their environments. 

- In some cases, domestic birds were reported to be sick or dead. 

- Where the information is available, the genetic sequence data from the viruses from the human cases closely matches that from recent local animal viruses and are identified as clade 2.3.2.1e viruses. 

- From the information available thus far on these recent human cases, there is no indication of human-tohuman transmission of the A(H5N1) viruses.  

A(H5N5), United States of America 

- On 15 November 2025, the United States of America (US) notified WHO of a confirmed human infection with influenza A(H5). 

- The patient was an adult with underlying medical conditions residing in Washington State. 

- The patient developed symptoms including fever during the week ending 25 October 2025. 

- During the week ending 8 November 2025, the patient was hospitalized with a serious illness and subsequently died on 21 November.  

- Respiratory specimens collected at the healthcare facility tested positive for influenza A virus by reverse-transcription-polymerase chain reaction (RT-PCR) and were presumptive positive for influenza A(H5) at the laboratory at the University of Washington. 

- The specimens were sent to the Washington State Public Health Laboratory, where influenza A(H5) was confirmed with the US Centers for Disease Control and Prevention (CDC) influenza A(H5) assay. 

- The sample was received at the CDC on 19 November. Sequencing conducted at the University of Washington and at the CDC indicated this was an influenza A(H5N5) virus belonging to the H5 haemagglutinin (HA) clade 2.3.4.4b.  

- Public health investigation revealed that the patient kept backyard poultry and domestic birds. 

- Additional epidemiological investigations were under way at the time of notification and included active monitoring of anyone who was in close contact with the patient.{7,8} 

- This is the first human case of this subtype reported globally. 

- Human infections with A(H5N1), A(H5N2), A(H5N6) and A(H5N8) have been reported previously. 

- A(H5N5) virus infections in animals have been detected and reported. 

- HPAI A(H5) clade 2.3.4.4b A(H5N5) viruses have been detected in North America in wild birds and wild mammals since at least 2023.{9} 

- According to reports received by WOAH, various influenza A(H5) subtypes continue to be detected in wild and domestic birds in Africa, the Americas, Asia and Europe. 

- Infections in non-human mammals are also reported, including in marine and land mammals.{10} 

- A list of bird and mammalian species affected by HPAI A(H5) viruses is maintained by FAO.{11}

-- Risk Assessment for avian influenza A(H5) viruses:  

1. What is the current global public health risk of additional human cases of infection with avian influenza A(H5) viruses?  

- Most human infections so far have been reported in people exposed to A(H5) viruses, for example, through contact with infected poultry or contaminated environments, including live poultry markets, and occasionally infected mammals and contaminated environments. 

- As long as the viruses continue to be detected in animals and related environments humans are exposed to, further human cases associated with such exposures are expected but remain unusual. 

- The impact for public health if additional sporadic cases are detected is minimal. 

- The current overall global public health risk of additional sporadic human cases is low. 

2. What is the likelihood of sustained human-to-human transmission of avian influenza A(H5) viruses related to the events above?  

- No sustained human-to-human transmission has been identified associated with the recent reported human infections with avian influenza A(H5) viruses. 

- There has been no reported human-to-human transmission of A(H5N1) viruses since 2007, although there may be gaps in investigations. 

- In 2007 and the years prior, small clusters of A(H5) virus infections in humans were reported, including some involving health care workers, where limited human-to-human transmission could not be excluded; however, sustained human-to-human transmission was not reported.  

- Current evidence suggests that influenza A(H5) viruses related to these events did not acquire the ability to efficiently transmit between people, therefore sustained human-to-human transmission is thus currently considered unlikely.  

3. What is the likelihood of international spread of avian influenza A(H5) viruses by travellers?  

- Should infected individuals from affected areas travel internationally, their infection may be detected in another country during travel or after arrival. 

- If this were to occur, further communitylevel spread is considered unlikely as current evidence suggests these viruses have not acquired the ability to transmit easily among humans.  

A(H9N2), China  

- Since the last risk assessment of 5 November 2025, China notified WHO of four cases of infection with influenza A(H9N2) on 6 November 2025 and three cases on 12 December 2025. 

- All but two cases were in children. 

- Cases were detected in Guangdong (one), Guangxi (three), Henan (one) and Hubei (two) provinces. 

- The cases had onsets of symptoms in September, October and November 2025. 

- Four cases had reported exposure to backyard poultry, two had exposure to live poultry markets and the source of exposure for one case was under investigation at the time of reporting. 

- All cases had mild illness and recovered, except one in an elderly person with underlying conditions who was hospitalized at the time of reporting with severe pneumonia. 

- No further cases were detected among contacts of these cases. 

- A(H9) viruses were detected in environmental samples collected during the investigations around some of the cases. 

-- Risk Assessment for avian influenza A(H9N2):   

- 1. What is the global public health risk of additional human cases of infection with avian influenza A(H9N2) viruses?   

- Most human cases follow exposure to the A(H9N2) virus through contact with infected poultry or contaminated environments. 

- Most human infections of A(H9N2) to date have resulted in mild clinical illness. 

- Since the virus is endemic in poultry in multiple countries in Africa and Asia, further human cases associated with exposure to infected poultry are expected but remain unusual. 

- The impact to public health if additional sporadic cases are detected is minimal. 

- The overall global public health risk of additional sporadic human cases is low.  

2. What is the likelihood of sustained human-to-human transmission of avian influenza A(H9N2) viruses related to this event?   

- At the present time, no sustained human-to-human transmission has been identified associated with the recently reported human infections with A(H9N2) viruses. 

- Current evidence suggests that A(H9N2) viruses from these cases did not acquire the ability of sustained transmission among humans, therefore sustained human-to-human transmission is thus currently considered unlikely.   

3. What is the likelihood of international spread of avian influenza A(H9N2) virus by travellers?   

- Should infected individuals from affected areas travel internationally, their infection may be detected in another country during travel or after arrival. 

- If this were to occur, further community level spread is considered unlikely as current evidence suggests the A(H9N2) virus subtype has not acquired the ability to transmit easily among humans.   

Swine influenza viruses in humans 

Influenza A(H1N1)v, China 

- Since the last risk assessment of 5 November 2025, the detection of a Eurasian avian-like swine influenza A(H1N1)v virus in a human was reported from China on 12 December 2025. 

- A 60-year-old male from Yunnan province had onset of mild illness on 2 November 2025, was hospitalized on 6 November and discharged on 10 November. 

- He had reported exposure to backyard pigs. 

Influenza A(H1N2)v, USA 

- A human case of infection with an influenza A(H1N2)v virus was detected in the state of Vermont in an adult who had an onset of symptoms in early October. 

- The individual was briefly hospitalized and has recovered. 

- The investigation conducted by state public health officials was unable to determine the likely source of exposure or if close contacts developed symptoms. 

- According to the report, no human-to-human transmission was identified associated with this case.{12}  

-- Risk Assessment:  

1. What is the public health risk of additional human cases of infection with swine influenza viruses?  

- Swine influenza viruses circulate in swine populations in many regions of the world. 

- Depending on geographic location, the genetic characteristics of these viruses differ. 

- Most human cases are exposed to swine influenza viruses through contact with infected animals or contaminated environments. 

- Human infection tends to result in mild clinical illness in most cases. 

- Since these viruses continue to be detected in swine populations, further human cases are expected. 

- The impact to public health if additional sporadic cases are detected is minimal. 

- The overall risk of additional sporadic human cases is low.  

2. What is the likelihood of sustained human-to-human transmission of swine influenza viruses?   

- No sustained human-to-human transmission was identified associated with the events described above. 

- Current evidence suggests that contemporary swine influenza viruses have not acquired the ability of sustained transmission among humans, therefore sustained human-to-human transmission is thus currently considered unlikely. 

3. What is the likelihood of international spread of swine influenza viruses by travelers?   

- Should infected individuals from affected areas travel internationally, their infection may be detected in another country during travel or after arrival. 

- If this were to occur, further community level spread is considered unlikely as current evidence suggests that these viruses have not acquired the ability to transmit easily among humans. 

Overall risk management recommendations: 

-- Surveillance and investigations

• Due to the constantly evolving nature of influenza viruses, WHO continues to stress the importance of global strategic surveillance in animals and humans to detect virologic, epidemiologic and clinical changes associated with circulating influenza viruses that may affect human (or animal) health. Continued vigilance is needed within affected and neighbouring areas to detect infections in animals and humans. Close collaboration with the animal health and environment sectors is essential to understand the extent of the risk of human exposure and to prevent and control the spread of animal influenza. WHO has published guidance on surveillance for human infections with avian influenza A(H5) viruses. 

• As the extent of influenza virus circulation in animals is not clear, epidemiologic and virologic surveillance and the follow-up of suspected human cases should continue systematically. Guidance on investigation of non-seasonal influenza and other emerging acute respiratory diseases has been published on the WHO website. 

• Countries should increase avian influenza surveillance in: 

- domestic and wild birds,

- enhance surveillance for early detection in cattle populations in countries where HPAI is known to be circulating, 

- include HPAI as a differential diagnosis in non-avian species, including cattle and other livestock populations, with high risk of exposure to HPAI viruses; 

- monitor and investigate cases in non-avian species, including livestock, report cases of HPAI in all animal species, including unusual hosts, to WOAH and other international organizations, 

- share genetic sequences of avian influenza viruses in publicly available databases, 

- implement preventive and early response measures to break the HPAI transmission cycle among animals through movement restrictions of infected livestock holdings and strict biosecurity measures in all holdings, 

- employ good production and hygiene practices when handing animal products, and protect persons in contact with suspected/infected animals.{13} 

- More guidance can be found from WOAH and FAO. 

- When there has been human exposure to a known outbreak of an influenza A virus in domestic poultry, wild birds or other animals – or when there has been an identified human case of infection with such a virus – enhanced surveillance in potentially exposed human populations becomes necessary. 

- Enhanced surveillance should consider the health care seeking behaviour of the population, and could include a range of active and passive health care and/or communitybased approaches, including: 

> enhanced surveillance in local influenza-like illness (ILI)/SARI systems, 

> active screening in hospitals and of groups that may be at higher occupational risk of exposure, and 

> inclusion of other sources such as traditional healers, private practitioners and private diagnostic laboratories. 

• Vigilance for the emergence of novel influenza viruses with pandemic potential should be maintained at all times including during a non-influenza emergency. In the context of the cocirculation of SARS-CoV-2 and influenza viruses, WHO has updated and published practical guidance for integrated surveillance. 

-- Notifying WHO 

• All human infections caused by a new subtype of influenza virus are notifiable under the International Health Regulations (IHR, 2005).{14} State Parties to the IHR (2005) are required to immediately notify WHO of any laboratory-confirmed{15} case of a recent human infection caused by an influenza A virus with the potential to cause a pandemic{16}. Evidence of illness is not required for this report. Evidence of illness is not required for this report. 

• WHO published the case definition for human infections with avian influenza A(H5) virus requiring notification under IHR (2005): https://www.who.int/teams/global-influenzaprogramme/avian-influenza/case-definitions. 

-- Virus sharing and risk assessment 

• It is critical that these influenza viruses from animals or from humans are fully characterized in appropriate animal or human health influenza reference laboratories. Under WHO’s Pandemic Influenza Preparedness (PIP) Framework, Member States are expected to share influenza viruses with pandemic potential on a timely basis{17} with a WHO Collaborating Centre for influenza of GISRS. The viruses are used by the public health laboratories to assess the risk of pandemic influenza and to develop candidate vaccine viruses.  

• The Tool for Influenza Pandemic Risk Assessment (TIPRA) provides an in-depth assessment of risk associated with some zoonotic influenza viruses – notably the likelihood of the virus gaining human-to-human transmissibility, and the impact should the virus gain such transmissibility. TIPRA maps relative risk amongst viruses assessed using multiple elements. The results of TIPRA complement those of the risk assessment provided here, and those of prior TIPRA analyses will be published at http://www.who.int/teams/global-influenza-programme/avian-influenza/toolfor-influenza-pandemic-risk-assessment-(tipra).  

-- Risk reduction 

• Given the observed extent and frequency of avian influenza in poultry, wild birds and some wild and domestic mammals, the public should avoid contact with animals that are sick or dead from unknown causes, including wild animals, and should report dead birds and mammals or request their removal by contacting local wildlife or veterinary authorities.  

• Eggs, poultry meat and other poultry food products should be properly cooked and properly handled during food preparation. Due to the potential health risks to consumers, raw milk should be avoided. WHO advises consuming pasteurized milk. If pasteurized milk isn’t available, heating raw milk until it boils makes it safer for consumption. 

• WHO has published practical interim guidance to reduce the risk of infection in people exposed to avian influenza viruses. 

-- Trade and travellers 

• WHO advises that travellers to countries with known outbreaks of animal influenza should avoid farms, contact with animals in live animal markets, entering areas where animals may be slaughtered, or contact with any surfaces that appear to be contaminated with animal excreta. Travelers should also wash their hands often with soap and water. All individuals should follow good food safety and hygiene practices.  

• WHO does not advise special traveller screening at points of entry or restrictions with regards to the current situation of influenza viruses at the human-animal interface. For recommendations on safe trade in animals and related products from countries affected by these influenza viruses, refer to WOAH guidance.  

Links:  

-- WHO Human-Animal Interface web page https://www.who.int/teams/global-influenza-programme/avian-influenza 

-- WHO Influenza (Avian and other zoonotic) fact sheet https://www.who.int/news-room/fact-sheets/detail/influenza-(avian-and-other-zoonotic) 

-- WHO Protocol to investigate non-seasonal influenza and other emerging acute respiratory diseases https://www.who.int/publications/i/item/WHO-WHE-IHM-GIP-2018.2 

-- WHO Public health resource pack for countries experiencing outbreaks of influenza in animals:  https://www.who.int/publications/i/item/9789240076884 

-- Cumulative Number of Confirmed Human Cases of Avian Influenza A(H5N1) Reported to WHO  https://www.who.int/teams/global-influenza-programme/avian-influenza/avian-a-h5n1-virus 

-- Avian Influenza A(H7N9) Information https://www.who.int/teams/global-influenza-programme/avian-influenza/avian-influenza-a-(h7n9)virus 

-- World Organisation of Animal Health (WOAH) web page: Avian Influenza  https://www.woah.org/en/home/ 

-- Food and Agriculture Organization of the United Nations (FAO) webpage: Avian Influenza https://www.fao.org/animal-health/avian-flu-qa/en/ 

-- OFFLU http://www.offlu.org/ 

___

{1} This summary and assessment covers information confirmed during this period and may include information received outside of this period. 

{2} For epidemiological and virological features of human infections with animal influenza viruses not reported in this assessment, see the reports on human cases of influenza at the human-animal interface published in the Weekly Epidemiological Record here.  

{3} World Organisation for Animal Health (WOAH). Avian influenza. Global situation. Available at: https://www.woah.org/en/disease/avian-influenza/#ui-id-2. 

{4} Food and Agriculture Organization of the United Nations (FAO). Global Avian Influenza Viruses with Zoonotic Potential situation update. Available at: https://www.fao.org/animal-health/situation-updates/global-aiv-withzoonotic-potential. 

{5} World Health Organization (2012). Rapid risk assessment of acute public health events. World Health Organization. Available at: https://iris.who.int/handle/10665/70810. 

{6} World Health Organization. Case definitions for the 4 diseases requiring notification to WHO in all circumstances under the International Health Regulations (2005). Case definitions for the four diseases requiring notification in all circumstances under the International Health Regulations (2005).   

{7} World Health Organization (5 December 2025). Disease Outbreak News; Avian Influenza A(H5N5)- United States of America. Available at: https://www.who.int/emergencies/disease-outbreak-news/item/2025DON590. 

{8} US CDC FluView. Weekly US Influenza Surveillance Report: Key Updates for Week 46, ending November 15, 2025. Available at https://www.cdc.gov/fluview/surveillance/2025-week-46.html. 

{9} Erdelyan CNG, Kandeil A, Signore AV, et al. Multiple transatlantic incursions of highly pathogenic avian influenza clade 2.3.4.4b A(H5N5) virus into North America and spillover to mammals. Cell Rep. 2024 Jul 23;43(7):114479. doi:10.1016/j.celrep.2024.114479. Epub 2024 Jul 13. PMID:39003741; PMCID:PMC11305400. 

{10}  World Organisation for Animal Health (WOAH). Avian influenza. Global situation. Available at: https://www.woah.org/en/disease/avian-influenza/#ui-id-2. 

{11} Food and Agriculture Organization of the United Nations. Global Avian Influenza Viruses with Zoonotic Potential situation update. Available at: https://www.fao.org/animal-health/situation-updates/global-aiv-withzoonotic-potential/bird-species-affected-by-h5nx-hpai/en. 

{12} US CDC FluView. Weekly US Influenza Surveillance Report: Key Updates for Week 46, ending November 15, 2025. Available at https://www.cdc.gov/fluview/surveillance/2025-week-46.html. 

{13} World Organisation for Animal Health. Statement on High Pathogenicity Avian Influenza in Cattle, 6 December 2024. Available at: https://www.woah.org/en/high-pathogenicity-avian-influenza-hpai-in-cattle/. 

{14} World Health Organization. Case definitions for the four diseases requiring notification in all circumstances under the International Health Regulations (2005). 

{15} World Health Organization. Manual for the laboratory diagnosis and virological surveillance of influenza (2011). Available at: https://apps.who.int/iris/handle/10665/44518. 

{16} World Health Organization. Pandemic influenza preparedness framework for the sharing of influenza viruses and access to vaccines and other benefits, 2nd edition. Available at: https://iris.who.int/handle/10665/341850. 

{17} World Health Organization. Operational guidance on sharing influenza viruses with human pandemic potential (IVPP) under the Pandemic Influenza Preparedness (PIP) Framework (2017). Available at: https://apps.who.int/iris/handle/10665/259402. 

___

Source: 

Link: https://www.who.int/publications/m/item/influenza-at-the-human-animal-interface-summary-and-assessment--19-december-2025

____

Avian #Influenza #H5N5 - #USA (#WHO D.O.N., Dec. 5 '25)

 

5 December 2025

Situation at a glance

On 15 November 2025, WHO was notified of the 71st confirmed human case with influenza A(H5) since early 2024 in the United States of America— the first human case reported in the United States of America since February 2025. 

On 20 November, U.S. Centers for Disease Control and Prevention (CDC) laboratory sequencing verified the virus as influenza A(H5N5), representing the first globally reported human case caused by an influenza A(H5N5) virus. 

The investigation by health authorities in the United States of America is ongoing. 

Contact tracing identified no further cases amongst contacts, and there is currently no evidence of human-to-human transmission. 

Due to the constantly evolving nature of influenza viruses, WHO continues to stress the importance of global surveillance to detect and monitor virological (including genomics), epidemiological and clinical changes associated with emerging or circulating influenza viruses that may affect human health and timely virus sharing for risk assessment. 

Based on available information, the WHO currently assesses the overall public health risk posed by A(H5) viruses as low. 

However, for individuals with occupational risk of exposure, the risk of infection is considered low to moderate.

Description of the situation

On 15 November 2025, WHO was notified of a confirmed human infection with influenza A(H5) in the United States of America—the first reported in the country since February 2025 and the 71st since early 2024. 

On 20 November, CDC laboratory sequencing verified the virus as influenza A(H5N5), representing the first human case of this subtype reported globally. 

The patient was an adult with underlying medical conditions residing in Washington State. 

The patient developed symptoms including fever during the week ending 25 October 2025. 

During the week ending 8 November 2025, the patient was hospitalized with a serious illness and subsequently died on 21 November.

Respiratory specimens collected at the healthcare facility tested positive for influenza A virus by RT-PCR and were presumptive positive for influenza A(H5) at the University of Washington. 

The specimens were sent to the Washington State Public Health Laboratory, where influenza A(H5) was confirmed using the CDC influenza A(H5) assay. 

The sample was received at the CDC on 19 November. 

Sequencing conducted at the University of Washington and at the CDC indicated this was an influenza A(H5N5) virus belonging to the H5 haemagglutinin (HA) clade 2.3.4.4b[1]. 

Public health investigation revealed that the patient kept backyard poultry and domestic birds. 

Additional epidemiological investigations are under way and include active monitoring of anyone who was in close contact with the patient.

Epidemiology

Animal influenza viruses typically circulate within animal populations, but some have the potential to infect humans. 

Human infections are predominantly acquired through direct contact with infected animals or exposure to contaminated environments. 

Based on the original host species, influenza A viruses can be categorized such as avian influenza, swine influenza, and other animal-origin influenza subtypes.

Human infection with avian influenza viruses may result in a spectrum of illness, ranging from mild upper respiratory tract symptoms to severe, life-threatening conditions. 

Clinical manifestations may include conjunctivitis, respiratory, gastrointestinal symptoms, encephalitis (brain swelling), and encephalopathy (brain damage). 

In some cases, asymptomatic infections with the virus have been reported in individuals with known exposure to infected animals and environments.

A definitive diagnosis of human avian influenza infection requires laboratory confirmation. 

WHO regularly updates its technical guidance on the detection of zoonotic influenza, utilizing molecular diagnostic methods such as RT-PCR. 

Clinical evidence indicates that certain antiviral agents, particularly neuraminidase inhibitors (e.g., oseltamivir, zanamivir), have been shown to shorten the duration of viral replication and improve patient outcomes in some cases. 

This antiviral agent should be administered within 48 hours of symptom onset.

High pathogenicity avian influenza A(H5) clade 2.3.4.4b A(H5N5) viruses have been detected in North America in wild birds and wild mammals since at least 2023.[2] 

This is the first laboratory-confirmed human infection with an influenza A(H5N5) virus in the United States of America and reported globally.

Public health response

The CDC and State public health officials have initiated several public health response measures: 

-- Public health officials are conducting surveillance in the area, that included additional case investigations and contact tracing.  

-- Since March 2024, at least 30,100 people have been monitored, and at least 1260 have been tested after exposure to infected animals in the USA. 

-- The CDC conducts enhanced routine surveillance to detect and monitor influenza activity, including infections caused by novel influenza viruses such as avian influenza A(H5).  

-- The CDC recommends that state and local public health departments monitor individuals exposed to birds or other animals (including livestock) suspected of being infected with avian influenza A viruses for the onset of signs and symptoms for up to 10 days after their last exposure. Individuals who develop signs or symptoms of respiratory illness and/or conjunctivitis should be tested for influenza.  

-- The CDC has issued recommendations for the public to avoid unprotected contact with sick or dead animals, including wild birds, poultry, other domestic fowl, and other wild or domestic animals, as well as animal droppings, litter, or materials contaminated by birds or other animals suspected of being infected with the influenza A(H5) virus. 

-- The CDC has interim recommendations for prevention, monitoring, and public health investigations of avian influenza A(H5) virus infections in people. The CDC has also updated recommendations for occupational protection and the use of personal protective equipment (PPE).  

WHO risk assessment

Human infections with avian influenza A(H5) viruses are considered unusual, as A(H5) viruses remain primarily avian influenza viruses. 

However, in rare cases, individuals exposed to infected animals or contaminated environments can become infected with A(H5) viruses.  

Influenza A(H5N5) viruses are detected in birds, including wild birds and domestic poultry, and sometimes in non-human mammals. 

When avian influenza viruses circulate in poultry populations, there is an inherent risk of human infection through exposure to infected birds or contaminated environments. 

As such, sporadic human cases are expected. 

The case had underlying conditions and subsequently died. 

The investigation by health authorities in the United States of America is ongoing and included contact tracing which identified no further cases amongst contacts, and there is currently no evidence of human-to-human transmission. 

This is the 71st confirmed human case of A(H5) in the United States of America since early 2024, and the first since February 2025. 

To date, no human-to-human transmission has been identified in any of the A(H5) cases reported in the United States of America. 

From a global perspective, while a few events with limited human-to-human transmission of zoonotic influenza A(H5) have been described between 1997 and 2007, sustained human-to-human transmission has not been detected to date. 

Based on available information, the WHO currently assesses the overall public health risk posed by A(H5) viruses as low. However, for individuals with occupational risk of exposure, the risk of infection is considered low to moderate.

The risk assessment will be updated as needed, based on any new epidemiological or virological information related to this event.  

WHO advice

This event does not change the current WHO recommendations on public health measures and surveillance of influenza.

Given the current situation of influenza viruses at the human-animal-environmental interface, WHO does not recommend special traveler screening at points of entry or any restrictions.

Due to the constantly evolving nature of influenza viruses, WHO continues to stress the importance of global surveillance to detect and monitor virological (including genomics), epidemiological and clinical changes associated with emerging or circulating influenza viruses that may affect human health and timely virus sharing for risk assessment.

When humans have been exposed to an influenza A virus outbreak in domestic poultry, wild birds, or other animals or when a human case of infection is identified, enhanced surveillance of potentially exposed human populations becomes necessary. This surveillance should consider the healthcare-seeking behaviour of the population and may include a range of active and passive approaches, such as enhanced surveillance in influenza-like illness (ILI)/severe acute respiratory infection (SARI) systems, active screening in hospitals, and among groups at higher occupational risk of exposure. It should also consider other sources, such as traditional healers, private practitioners, and private diagnostic laboratories.

Given the observed widespread occurrence of avian influenza in poultry, wild birds and some wild and domestic mammals, the public should avoid contact with any sick or dead animals. 

Individuals should report deceased birds and mammals or request their removal by contacting local wildlife or veterinary authorities. 

Eggs, poultry meat, and other poultry products should be properly cooked and handled during food preparation. 

Due to potential health risks, consumption of raw milk should be avoided. WHO advises consuming pasteurized milk and if pasteurized milk is not available, heating raw milk until it boils makes it safer for consumption.

In the case of a confirmed or suspected human infection caused by a novel influenza A virus with pandemic potential, including avian influenza viruses, early clinical management, a thorough epidemiologic investigation of animal exposure history, travel, and contact tracing should be conducted even while awaiting the confirmatory laboratory results. 

The epidemiologic investigation should also include early identification of unusual events that could signal person-to-person transmission of the novel virus. 

Clinical samples collected from confirmed or suspected cases should be tested and sent to a WHO Collaborating Center[3] for further characterization. Additional samples should be collected from animals, the environment or any foods suspected to be sources of infection.

WHO advises travelers to countries with known animal influenza outbreaks to avoid farms, live animal markets, areas where animals may be slaughtered and contact with any surfaces potentially contaminated by animal feces. 

Travelers should also wash their hands frequently with soap and water and should follow good food safety and good food hygiene practices. 

If infected individuals from affected areas travel internationally, their infection may be detected either during travel or upon arrival. However, further community level spread is considered unlikely, as this virus has not yet acquired the ability to transmit easily among humans.

Poultry workers should take additional health precautions as they are at higher risk of exposure to avian influenza and other zoonotic diseases due to their close contact with birds and potentially contaminated environments. Farm workers who have direct or close contact with animals or materials infected or contaminated with avian influenza A(H5) virus, should wear appropriate personal protective equipment (PPE) to minimize their risk of exposure.

All human infections caused by a novel influenza A virus subtype are notifiable under the International Health Regulations (IHR,2005) and State Parties to the IHR are required to immediately notify WHO within 24 hours of any laboratory-confirmed case of a recent human infection caused by an influenza A virus due to the potential to cause a pandemic. Evidence of illness is not required for this report. WHO has updated the influenza A(H5) confirmed case definition on the WHO website. 

Currently, there are no readily available vaccines against influenza A(H5) virus for humans. Candidate vaccine viruses for pandemic preparedness have been selected against several A(H5) clades. Existing seasonal influenza vaccines are unlikely to provide protection to against avian influenza A(H5) viruses, based on currently available data. Close monitoring of the epidemiological situation and serological investigations are essential for assessing risk and adjusting risk management measures as needed..

WHO does not recommend any restriction on travel to or trade with the United States of America, based on the information available on the current event.  

Further information

-- Centers for Disease Control and Prevention (CDC). H5 Bird Flu: Current Situation. Available from: https://www.cdc.gov/bird-flu/situation-summary/index.html  

-- Centers for Disease Control and Prevention (CDC). Weekly US Influenza Surveillance Report: Key Updates for Week 46, ending November 15, 2025. Available from: https://www.cdc.gov/fluview/surveillance/2025-week-46.html  

-- World Health Organization, Food and Agriculture Organization of the United Nations, & World Organization for Animal Health (July 2025). Updated joint FAO/WHO/WOAH assessment of recent influenza A(H5N1) virus events in animals and people. WHO, FAO, WOAH; 2025. Available from: https://cdn.who.int/media/docs/default-source/influenza/human-animal-interface-risk-assessments/fao-woah-who-joint-h5-assessment-july-2025.pdf?sfvrsn=fe76b74e_1&download=true

-- World Health Organization. Cumulative number of confirmed human cases of avian influenza A(H5N1) reported to WHO. Geneva: WHO; 2025. Available from: https://www.who.int/publications/m/item/cumulative-number-of-confirmed-human-cases-for-avian-influenza-a(h5n1)-reported-to-who--2003-2025--5-november-2025

-- United States Department of Agriculture, Animal and Plant Health Inspection Service. The Occurrence of Another Highly Pathogenic Avian Influenza (HPAI) Spillover from Wild Birds into Dairy Cattle. Washington, D.C.: USDA; 2025.  Available from: https://www.aphis.usda.gov/sites/default/files/dairy-cattle-hpai-tech-brief.pdf  

-- Centers for Disease Control and Prevention. Recommended composition of influenza virus vaccines for use in the southern hemisphere 2025 influenza season and development of candidate vaccine viruses for pandemic preparedness. Atlanta: CDC; 2025. Available from: https://cdn.who.int/media/docs/default-source/vcm-southern-hemisphere-recommendation-2025/202409_qanda_recommendation_final.pdf?sfvrsn=bd3d90b1_3  

-- Pan American Health Organization / World Health Organization. Epidemiological Alert - Human infections caused by avian influenza A(H5N1) in the Region of the Americas - 5 June 2024. Washington, D.C.: PAHO/WHO; 2024. Available from: https://www.paho.org/en/documents/epidemiological-alert-human-infections-caused-avian-influenza-ah5n1-region-americas-5 

-- Public Health Risk Assessment associated with the spread of zoonotic avian influenza A(H5N1) clade 2.3.4.4b in the Region of the Americas - 12 July 2024. Available from: https://www.paho.org/en/documents/public-health-risk-assessment-associated-spread-zoonotic-avian-influenza-ah5n1-clade  

-- World Health Organization. Mosaic Respiratory Surveillance Framework. Geneva: WHO; 2024. Available from: https://www.who.int/initiatives/mosaic-respiratory-surveillance-framework/ 

-- World Health Organization. Practical interim guidance to reduce the risk of infection in people exposed to avian influenza viruses. Geneva: WHO; 2024. Available from: https://www.who.int/publications/i/item/B09116  

-- World Health Organization. WHO case definition for human infections with avian influenza A(H5) virus requiring notification under IHR (2005) Geneva: WHO; 2024. Available from: https://www.who.int/teams/global-influenza-programme/avian-influenza/case-definitions 

-- World Health Organization. Surveillance for human infections with avian influenza A(‎H5)‎ viruses: objectives, case definitions, testing and reporting. Geneva: WHO; 2024. Available from: https://www.who.int/publications/i/item/B09337

-- World Health Organization. Case definitions for the four diseases requiring notification in all circumstances under the International Health Regulations (2005). Geneva: WHO; 2024. Available from: https://cdn.who.int/media/docs/default-source/documents/emergencies/case-definitions-ihr-four-diseases7f1ee707-3d13-4581-a1af-d5f44f86423a.pdf?sfvrsn=9c68df20_1&download=true  

-- Animal and Plant Health Inspection Service. Confirmation of Highly Pathogenic Avian Influenza in Commercial and Backyard Flocks. Available from: Avian Influenza | Animal and Plant Health Inspection Service (usda.gov)   

-- United States Department of Agriculture, Animal and Plant Health Inspection Service. Detections of Highly Pathogenic Avian Influenza in Mammals. Washington, D.C.: USDA; 2025.  Available from: https://www.aphis.usda.gov/livestock-poultry-disease/avian/avian-influenza/hpai-detections/mammals 

-- United States Department of Agriculture. Animal and Plant Health Inspection Service. HPAI Confirmed Cases in Livestock. Washington, D.C.: USDA; 2024. Available from: https://www.aphis.usda.gov/livestock-poultry-disease/avian/avian-influenza/hpai-detections/hpai-confirmed-cases-livestock 

-- Pan American Health Organization / World Health Organization.  Informe sobre el Grupo de Expertos para la CIPCIZA - Reunión de grupos de trabajo: Vigilancia, Laboratorio y Evaluación de riesgos intersectorial. Washington, D.C.: PAHO/WHO; 2025. Available from: https://www.paho.org/es/documentos/informe-sobre-grupo-expertos-para-cipciza-reunion-grupos-trabajo-vigilancia-laboratorio  

-- Pan American Health Organization / World Health Organization. Colocación y retiro de EPP en trabajadores de granjas ante influenza aviar. Washington, D.C.: PAHO/WHO; 2025. Available from: https://www.paho.org/es/documentos/colocacion-retiro-epp-trabajadores-granjas-ante-influenza-aviar . 

-- Pan American Health Organization / World Health Organization. Colocación y retiro de EPP en trabajadores de la salud ante influenza aviar. Washington, D.C.: PAHO/WHO; 2025. Available from: https://www.paho.org/es/documentos/colocacion-retiro-epp-trabajadores-salud-ante-influenza-aviar. 

-- Pan American Health Organization / World Health Organization. Influenza at the Human-Animal Interface: PAHO Recommendations to Strengthen Intersectoral Work for Surveillance, Early Detection, and Investigation, 9 July 2020. Available from: https://iris.paho.org/handle/10665.2/52563 

-- Pan American Health Organization / World Health Organization. Samples from patients suspected of Influenza A/H5 LABORATORY TESTING ALGORITHM. Available from: https://www.paho.org/en/documents/samples-patients-suspected-influenza-ah5-laboratory-testing-algorithm 

-- Pan American Health Organization / World Health Organization. Technical note: Laboratory Diagnosis of Human Infection with Influenza A/H5. Available from: https://www.paho.org/en/documents/technical-note-laboratory-diagnosis-human-infection-influenza-ah5 

-- Current technical information including monthly risk assessments at the Human-Animal Interface. Available from:  https://www.who.int/teams/global-influenza-programme/avian-influenza/monthly-risk-assessment-summary  

-- WHO. Zoonotic Influenza Outbreak Toolbox. Available from: https://www.who.int/emergencies/outbreak-toolkit/disease-outbreak-toolboxes/zoonotic-influenza-outbreak-toolbox

-- WHO. International Health Regulations (2005). Available from: http://www.who.int/ihr/publications/9789241596664/en/

-- WHO. Manual for the laboratory diagnosis and virological surveillance of influenza (2011). Available from: https://www.who.int/publications/i/item/manual-for-the-laboratory-diagnosis-and-virological-surveillance-of-influenza  

-- Terms of Reference for National Influenza Centers of the Global Influenza Surveillance and Response System. Available from: https://www.who.int/initiatives/global-influenza-surveillance-and-response-system/national-influenza-centres  

-- Pan American Health Organization / World Health Organization. Epidemiological Update: Avian Influenza A(H5N1) in the Americas Region, 15 November 2024. Washington, D.C.: PAHO/WHO; 2024. Available from: https://www.paho.org/en/documents/epidemiological-update-avian-influenza-ah5n1-americas-region-15-november-2024  

-- Pan American Health Organization / World Health Organization. Report of the Regional Consultation for the Strengthening of Intersectoral Work in the Human-Animal Interface of Influenza. 22 March 2023. Washington, D.C.: PAHO/WHO; 2023. Available from: Report of the Regional Consultation for the Strengthening of Intersectoral Work in the Human-Animal Interface of Influenza. March 2023 - PAHO/WHO | Pan American Health Organization 

-- Pan American Health Organization / World Health Organization. Strengthening the intersectoral work for Influenza at the Human Animal Interface in the Region of the Americas: Technical Questions and Answers. 19 May 2023. Washington, D.C.: PAHO/WHO; 2023. Available from: Strengthening the intersectoral work for Influenza at the Human Animal Interface in the Region of the Americas: Technical Questions and Answers - PAHO/WHO | Pan American Health Organization 

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[1] Lam TT, Davis CT, WHO/WOAH/FAO H5 Evolution Working Group. Nomenclature updates to the hemagglutinin gene clade designations resulting from the continued evolution of high pathogenicity avian influenza A(H5) virus clades 2.3.2.1c and 2.3.4.4. bioRxiv. 2025 Nov 23;2025.11.23.690055. doi:10.1101/2025.11.23.690055.

[2] Erdelyan CNG, Kandeil A, Signore AV, et al. Multiple transatlantic incursions of highly pathogenic avian influenza clade 2.3.4.4b A(H5N5) virus into North America and spillover to mammals. Cell Rep. 2024 Jul 23;43(7):114479. doi:10.1016/j.celrep.2024.114479. Epub 2024 Jul 13. PMID:39003741; PMCID:PMC11305400

[3] World Health Organization. WHO Collaborating Centres and Essential Regulatory Laboratories in the Global Influenza Surveillance and Response System (GISRS) [Internet]. Geneva: WHO; 2025. Available from: https://www.who.int/initiatives/global-influenza-surveillance-and-response-system/who-collaboration-center-erl

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Citable reference: World Health Organization (5 December 2025). Disease Outbreak News; Avian Influenza A(H5N5)- United States of America. Available at: https://www/who.int/emergencies/disease-outbreak-news/item/2025-DON590

Source: 

Link: https://www.who.int/emergencies/disease-outbreak-news/item/2025-DON590

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