Detection of #Divergent Highly Pathogenic Avian #Influenza #H5N1 Clade 2.3.4.4b Virus, São Paulo, #Brazil, 2025

 

Abstract

In 2025, we detected highly pathogenic avian influenza H5N1 virus in dead waterfowl at Ibirapuera Park, São Paulo, Brazil. Genomic characterization indicated a reassortant virus that emerged from locally circulating low pathogenicity avian influenza viruses and highly pathogenic North American lineages. Our results highlight cross-species transmission risk and underscore the need for enhanced surveillance.

Source: 

Link: https://doi.org/10.3201/eid3210.260723

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# Influenza at #human - #animal #interface - Summary and #risk #assessment, from 13 June to 7 July 2026 (WHO): 1 new case of #H5 virus, 2 of #H9N2 and one of #H3N2v

 

Influenza at the human-animal interface - Summary and risk assessment, from 13 June to 7 July 2026 {1} 

    • New human cases {2}: 

        ° From 13 June to 7 July 2026, based on reporting date, detections of influenza A(H5) in one human, influenza A(H9N2) in two humans, and an influenza A(H3N2) variant ((H3N2)v) virus in one human were officially reported. 

    • 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}: 

        ° There have been no reports of sustained human-to-human transmission 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 - At present, these viruses are not thought to be capable of sustained human-to-human transmission, although this could change as they evolve. 

        ° 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 

A(H5), Bangladesh   

    ° On 15 June 2026, Bangladesh notified WHO of one laboratory-confirmed human case of avian influenza A(H5) infection in Bangladesh in a child from Sylhet Division. 

    ° The case was detected notified through the National Influenza Surveillance, Bangladesh (NISB) platform as an influenza likeillness (ILI) case.    

    ° The patient developed respiratory symptoms on 17 May 2026, received outpatient healthcare on 20 May. 

    ° A clinical sample was collected that day and was received by the Institute of Epidemiology, Disease Control and Research (IEDCR) on 4 June as part of routine surveillance. 

    ° The sample tested positive for influenza A(H5) virus by real-time reverse transcription polymerase chain reaction (RTPCR) on 11 June.    

    ° The patient is now in good health and reported no travel history and no history of exposure to poultry. 

    ° However, poultry deaths were reported in the area surrounding the patient’s residence. 

    ° The outbreak investigation team identified and followed close and possible contacts. 

    ° Samples from some of the close contacts as well as animal and environmental samples were collected for testing for influenza. 

    ° All contacts remained asymptomatic and all samples tested negative for influenza.    

    ° This is the third laboratory-confirmed human case of avian influenza A(H5) reported in Bangladesh in 2026, and the 15th human case of avian influenza A(H5) reported to WHO from Bangladesh since 2008, including two fatal cases, one reported in 2013 and one in 2026.  

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 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.    
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  

    ° Between 12 and 23 June 2026, two laboratory-confirmed cases of A(H9N2) virus infection were detected in China. 

    ° Both cases had mild illness and were hospitalized in isolation wards at the time of reporting. 

{Click on Image to Enlarge}

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    ° Both cases had exposure to local live bird markets. 

    ° Samples from environments associated with the likely area of exposure of the cases tested positive for A(H9) viruses. 

    ° No further cases were detected among contacts of these 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, additional human cases associated with exposure to infected poultry or contaminated environments are expected but remain unusual. 
• The impact to public health if additional sporadic cases are detected is minimal. 
• The overall global public health risk is low.  
2. What is the likelihood of sustained human-to-human transmission of avian influenza A(H9N2) viruses related to these events?  
• 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.  
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(H3N2)v, Brazil  

    ° On 25 June 2026, Brazil notified PAHO/WHO of a laboratory-confirmed human infection with an influenza A(H3N2)v virus detected in a child in Santa Catarina state. 

    ° The patient had symptom onset on 12 June 2026 and due to worsening respiratory symptoms, healthcare was sought on 16 June. 

    ° The patient was referred for hospital admission with a diagnosis of Severe Acute Respiratory Infection (SARI). 

    ° Upon admission, an antigen test confirmed influenza A and the patient was placed in a private respiratory isolation room and antiviral treatment was initiated. 

    ° The patient was discharged on 19 June.  

    ° A nasopharyngeal swab sample was collected on 16 June and sent to the State public health laboratory for real-time RT-PCR. 

    ° On 18 June, a swine-origin influenza H3 variant was suspected, and the sample was sent to the Laboratory of Respiratory Viruses, Exanthems, Enteroviruses, and Viral Emergencies (LVRE) at the Oswaldo Cruz Institute (Fiocruz/Rio de Janeiro) on 19 June. 

    ° Analyses confirmed the presence of an influenza A(H3N2)v virus via molecular testing and genomic sequencing. 

    ° An investigation by the state and municipality epidemiological surveillance team found that all contacts were asymptomatic before, during and after the child’s illness. 

    ° The child's grandfather worked at a swine nursery housing approximately 5,000 animals, though he noted that sanitary barriers were in place. 

    ° The child frequently visited the grandfather's home and had contact with him several days a week.  

    ° This is the first human A(H3N2)v infection detected in the Brazil in 2026 and the first case reported in the state of Santa Catarina. 

Risk assessment for swine influenza viruses:    

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 event described above. 
• Current evidence suggests that contemporary swine influenza viruses have not acquired the ability of sustained transmission among humans.   
3. What is the likelihood of international spread of swine influenza 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 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.{7} 

            - 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).{8,9} State Parties to the IHR (2005) are required to immediately notify WHO of any laboratory-confirmed {10} case of a recent human infection caused by an influenza A virus with the potential to cause a pandemic {11}. 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 {12} 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 risk elements. The results of TIPRA complement those of the risk assessment provided here, and those of prior TIPRA risk assessments are published at http://www.who.int/teams/global-influenza-programme/avianinfluenza/tool-for-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/ 

° WOAH/FAO Network of Expertise on Animal Influenza (OFFLU) http://www.offlu.org/ 

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{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 four diseases requiring notification in all circumstances under the International Health Regulations (2005). Available at: https://www.who.int/publications/m/item/case-definitions-for-the-four-diseases-requiring-notification-towho-in-all-circumstances-under-the-ihr-(2005).  

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

{8} World Health Organization. International Health Regulations (2005), as amended through resolutions WHA67.13 (2014), WHA75.12 (2022), and WHA77.17 (2024) (https://apps.who.int/gb/bd/pdf_files/IHR_20142022-2024-en.pdf). 

{9} World Health Organization. Case definitions for the four diseases requiring notification in all circumstances under the International Health Regulations (2005) (https://www.who.int/publications/m/item/casedefinitions-for-the-four-diseases-requiring-notification-to-who-in-all-circumstances-under-the-ihr-(2005)). 

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

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

{12} World Health Organization. Operational guidance on sharing influenza viruses with human pandemic potential (IVPP) under the Pandemic Influenza Preparedness (PIP) Framework (2017) (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--7-july-2026

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#Genomic #Surveillance Uncovers the Silent #Spread of Avian #Influenza Virus #H5N1 2.3.4.4b Among Wild #Birds and #Mammals Along #Brazil’s Southern Coast

 

Abstract

Avian influenza viruses (AIVs) are widely distributed and have a wide range of hosts. Recently, the number of cases of infection associated with the circulation of highly pathogenic avian influenza H5N1 2.3.4.4b has raised concerns about its high transmission capacity in birds and mammals. This study analyzed swabs from bird and mammal species from the coast of Paraná and the northwest region of São Paulo, Brazil, for the presence of AIV in animals that did not present clinical or histopathological lesions of infection that indicated the need for molecular characterization during monitoring. Of the 661 animals analyzed, three tested positive, two of which were birds (Sula leucogaster and Thalasseus acuflavidus) while one was a mammal (Otaria flavescens) (0.45%, CI 95%: 0.16–1.33). A complete genome sequence of H5N1 AIV was obtained from a brown booby (Sula leucogaster) from the Paraná coast (GISAID accession number: EPI_ISL_1897537). Our study reinforces the importance of continuous genomic surveillance, especially in AIV hosts that do not show signs of infection, to enhance the One-Health assessment approach.

Source: Viruses, https://www.mdpi.com/journal/viruses

Link: https://www.mdpi.com/1999-4915/18/7/738

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Detection of #H5N1-Related #PB1 Sequences in a Low Pathogenic #H11N2 Virus from South #American Migratory #Shorebirds

 

Abstract

Highly pathogenic avian influenza (HPAI) A(H5N1) viruses of clade 2.3.4.4b have recently spread across the Americas, prompting intensified surveillance efforts in Brazil aimed at early detection in wild birds. As part of these efforts, we identified a low pathogenic avian influenza A(H11N2) virus in a white-rumped sandpiper (Calidris fuscicollis) sampled at Lagoa do Peixe National Park (PNLP) in southern Brazil. Whole-genome sequencing revealed that seven of the eight gene segments shared high nucleotide similarity (approximately 98.8%) with viruses previously detected in shorebirds from Delaware Bay, North America. In contrast, the PB1 segment showed high nucleotide similarity (approximately 99%) to the PB1 lineage associated with clade 2.3.4.4b A(H5N1) genotype B3.2 viruses circulating in the Americas. Phylogenetic, nucleotide identity, and molecular clock analyses indicated that this lineage shares a recent common ancestor with North American LPAI viruses and was subsequently detected in distinct viral genetic backgrounds. Although no HPAI virus was identified in this study, the presence of a PB1 segment related to H5N1-associated lineages suggests that genetic components linked to these viruses were circulating among low pathogenic avian influenza viruses in South America. These findings highlight the importance of continued surveillance in migratory bird populations to improve understanding of avian influenza virus diversity and support epidemiological monitoring.

Source: 

Link: https://www.mdpi.com/1999-4915/18/7/710

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Epidemiological study of #hantavirus in Southern #Brazil, 2009-2019

 

ABSTRACT

Brazil has the highest number of hantavirus cardiopulmonary syndrome cases on the American continent, with Santa Catarina being the state with the most notifications. This retrospective longitudinal study aimed to describe the epidemiological profile of 177 hantavirus cases reported in Santa Catarina from 2009 to 2019, using data from the Notifiable Diseases Information System (SINAN). Statistical analyses of socio-demographic, clinical, and epidemiological data revealed that the typical patient was a male of working age with low educational attainment, living in a rural area. The highest incidence occurred in the Santa Catarina West, Midwest, and Mountain regions, strongly associated with agricultural activities. The case fatality rate (CFR) was highest among the 15-19-year age group. Clinical risk factors for death included respiratory signs, increased hematocrit, and the need for mechanical ventilation. Patients who sought early care had a higher CFR, possibly due to the initial difficulty of differentiating hantavirus from other viral diseases. Conversely, regions with higher notification rates showed lower CFRs, suggesting better surveillance. This study highlights critical areas for public health intervention and the key characteristics of hantavirus patients (males in rural areas and adolescents aged 15-19 years in regions with low notification rates) and areas for public health intervention. Training for medical professionals in regions with low notification rates should aim to reduce lethality, especially in regions with low reported cases (Itajai river delta and South), where underreporting may be occurring. Furthermore, the high lethality in adolescents and in patients with non-specific initial symptoms requires greater awareness. This study shows the utility of a governmental database in identifying epidemiological patterns and creating public health strategies tailored to regional specificities.

Source: 

Link: https://www.scielo.br/j/rimtsp/a/VB7LM8DjmVJ9yJBwYzSjzMh/?lang=en

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#Influenza at human-animal interface - Summary & #risk #assessment (23 Jan. - 31 March 2026) (WHO, Apr. 29 '26): #H5N1, #H9N2, #H10N3, #H1N1v, #H3N2v cases reported

 

New human cases {2}: 

-- From 23 January to 31 March 2026, based on reporting date, detections of  influenza A(H5N1) in four humans, influenza A(H9N2) in five humans, influenza A(H10N3) in one human, an influenza A(H1N1) variant ((H1N1)v) virus in one human, an influenza A(H1N2)v virus in one human, and influenza A(H3N2)v virus in one human were reported officially. 

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.  

Risk management: 

-- Candidate vaccine viruses (CVVs) for zoonotic influenza viruses for pandemic preparedness purposes were reviewed and updated at the February 2026 WHO consultation on influenza vaccine composition for use in the northern hemisphere 2026-2027 influenza season. 

-- A detailed summary of zoonotic influenza viruses characterized since September 2025 is published here and updated CVVs lists are published here.  

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 22 January 2026, four laboratory-confirmed human cases of A(H5N1) infection were detected in Bangladesh (one case) and Cambodia (three cases).  

-- A(H5N1), Bangladesh  

- On 9 February 2026, the National International Health Regulations Focal Point of Bangladesh notified WHO of a laboratory-confirmed human case of avian influenza A(H5) infection in a child from Chattogram Division. 

- The patient, with no known comorbidities, developed symptoms on 21 January 2026 and was admitted to hospital on 28 January.  

- A nasopharyngeal swab was collected on 29 January as part of the Hospital-based Influenza Surveillance (HBIS) platform for influenza-like illness (ILI) and severe acute respiratory infection (SARI) sentinel surveillance in Bangladesh. 

- The patient was referred to a specialized private hospital and admitted to intensive care on 31 January. 

- The patient died on 1 February.  

- On 7 February, the Institute of Epidemiology, Disease Control and Research (IEDCR), serving as the National Influenza Centre (NIC), received and tested the sample, confirming influenza A(H5) by realtime reverse transcription polymerase chain reaction (RT-PCR) on the same day. 

- Virus characterization and whole genome sequencing was conducted at International Centre for Diarrhoeal Disease Research, Bangladesh (icddr,b), which confirmed that the A(H5N1) virus belongs to clade 2.3.2.1a of highly pathogenic avian influenza A(H5N1) virus (Gs/GD lineage), similar to the clade of viruses circulating in local poultry since around 2011. 

- Genetic sequence data are available in GISAID (EPI_ISL_20367262; submission date 19 Feb 2026; Institute of Epidemiology, Disease Control & Research (IEDCR)). 

- The case had exposure to household poultry, with two ducks and one chicken reportedly dying shortly before the case’s illness onset. 

- Animal and environmental samples were collected and tested with RT-PCR and serology by the zoonotic investigation team of icddr,b. 

- Two samples from ducks in the community and two samples from chicken meat in the freezer of household tested positive for influenza A(H5). 

- Samples from symptomatic close human contacts tested negative for influenza.  

- This is the first confirmed human case of avian influenza A(H5) reported in Bangladesh in 2026. 

- In 2025, four human cases of avian influenza A(H5) were reported.  

- 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.{7} 

- A list of bird and mammalian species affected by HPAI A(H5) viruses is maintained by FAO.{8}   

-- A(H5N1), Cambodia 

- Between 15 February and 31 March 2026, Cambodia notified WHO of three laboratory-confirmed cases of A(H5N1) virus infection. 

(...)

- All cases above had exposure to sick or dead backyard poultry. 

- The first case was detected through SARI surveillance. 

- The other two cases were detected following the detection of A(H5N1) in sick and dead poultry which initiated deployment of rapid response teams from the public health sector and active case finding. 

- The last case was identified as having had exposure to sick and dead poultry, sampled and then developed ILI symptoms. 

- Three human infections with A(H5N1) viruses have been confirmed in Cambodia in 2026 and none have been fatal. 

- Influenza A(H5N1) viruses continue to be detected in domestic birds in Cambodia in 2026, including in areas where human cases have been detected.{9} 

- 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-to-human transmission of the A(H5N1) viruses.   

-- A(H9N2), China  

- Between 9 February and 20 March 2026, China notified WHO of four laboratory-confirmed cases of A(H9N2) virus infection. 

(...)

-- A(H9N2), Italy, ex-Senegal {10} 

- On 21 March 2026, Italy notified WHO of the detection of A(H9N2) virus in an adult male. 

- The case had travelled to Senegal for more than six months and returned to Italy in mid-March 2026. 

- Upon arrival in Italy, the case sought medical care, presenting with fever and persistent cough that had been present since mid-January. 

- Laboratory investigations conducted on a bronchoalveolar lavage specimen on 16 March showed a positive Mycobacterium tuberculosis result, as well as detection of an un-subtypeable influenza A virus. 

- The case was admitted to an isolation room under airborne precautions in a negative-pressure room and received antitubercular and antiviral treatment. 

- As of 24 March, the patient was clinically stable and improving.  

- On 20 March 2026, the regional reference laboratory confirmed the A(H9) subtype, and on 21 March, influenza A(H9N2) was confirmed by next-generation sequencing. 

- Initial genetic findings suggest the infection was likely acquired from an avian source linked to Senegal. 

- Additional samples have been sent to Italy’s National Influenza Center, where further characterization confirmed virus subtype Influenza A(H9N2), with close genetic similarity to strains previously identified in poultry in Senegal. 

- No direct exposure to animals, wildlife or rural environments was identified. 

- There was also no reported contact with symptomatic or confirmed human cases. 

- Further epidemiological investigations on the source of exposure are ongoing. 

- Contacts identified in Senegal were asymptomatic. 

- All identified and traced contacts in Italy have tested negative for influenza and completed the period of active monitoring for the onset of symptoms and the quarantine required by national guidelines. 

- Human infections with influenza A(H9) viruses have been reported from countries in Africa and Asia, where these viruses are also detected in poultry. 

- This is the first imported human case of avian influenza A(H9N2) reported in the European Region. 

-- 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, additional human cases associated with exposure to infected poultry or contaminated environments are expected but remain unusual. 

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

The overall global public health risk is low.  

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

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, such as in the case reported by Italy. 

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.  

-- A(H10N3), China  

- On 9 February 2026, China notified WHO of one laboratory-confirmed case of human infection with an avian influenza A(H10N3) virus in a 34-year-old man from Guangdong province who developed symptoms on 29 December 2025. 

- On 1 January 2026, he was admitted to hospital and diagnosed with severe pneumonia, severe acute respiratory distress syndrome (ARDS) and sepsis. 

- Oseltamivir treatment was initiated on 3 January. 

- The patient's condition was stable at the time of reporting. 

- On 12 January, the sample was sent to the provincial laboratory for testing. 

- The result was positive for A(H10N3). On 14 January, the National Influenza Center confirmed the positive result.    

- The patient works near two establishments that keep live poultry on the premises and chickens are present at the household. 

- Environmental samples collected from sites related to likely poultry exposure, including the patient's home, the workplace and a nearby poultry market tested negative for A(H10N3) influenza virus. 

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

- A total of 98 close contacts of the patient were traced.  

- Since 2021, a total of seven cases of human avian influenza A(H10N3) virus infection have been reported globally and all were from China.   

-- Risk Assessment for avian influenza A(H10N3):   

- 1. What is the global public health risk of additional human cases of infection with avian influenza  A(H10N3) viruses?   

Human infections with avian influenza A(H10) viruses have been detected and reported previously.   

The circulation and epidemiology of these viruses in birds have been previously reported.{12} 

Avian influenza A(H10N3) viruses with different genetic characteristics have been detected previously in wild birds since the 1970s and more recently spilled over to poultry in some countries. 

As long as the virus continues to circulate in birds, further human cases can be 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(H10N3)   viruses?   

No sustained human-to-human transmission has been identified associated with the event described above or past events with human cases of influenza A(H10N3) viruses. 

Current epidemiologic and virologic evidence suggests that contemporary influenza A(H10N3) viruses assessed by the Global Influenza Surveillance and response System (GISRS) 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 avian influenza A(H10N3) 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 based on current limited evidence.  

Swine influenza viruses in humans  

-- Influenza A(H1N1)v, China  

- On 20 March 2026, China notified WHO of a laboratory-confirmed case of A(H1N1)v influenza virus infection in a child from Yunnan province. 

- The patient had onset of illness on 30 January 2026, was hospitalized on 2 February with pneumonia, and recovered in a few days. 

- The patient had reported exposure to domestic pigs prior to illness onset.  

-- Influenza A(H1N2)v, China 

- On 3 February 2026, China notified WHO of a laboratory-confirmed case of A(H1N2)v influenza virus infection in a child from Yunnan province. 

- The patient had onset of mild illness on 20 January 2026, and the infection was laboratory-confirmed on 2 February 2026. 

- The patient had reported exposure to domestic pigs prior to illness onset. This case and the one above are not epidemiologically linked.  

-- Influenza A(H3N2)v, Brazil 

- On 26 January 2026, Brazil notified WHO of a laboratory-confirmed case of A(H3N2)v influenza virus infection. 

- On 1 September 2025, a male child residing in the state of Mato Grosso do Sul presented with ILI symptoms and was taken to a health unit on 2 September. 

- The patient had no reported comorbidities or recent travel history and reported being vaccinated against seasonal influenza in the last campaign. 

- On 9 September, a respiratory sample was collected at the health unit, which is a sentinel unit for ILI. 

- On 12 September, the Central Public Health Laboratory of Mato Grosso do Sul (Lacen/MS) reported that the RT-qPCR test for influenza A virus subtyping amplified the influenza A marker along with the H3 marker, indicating a swine-origin variant of the influenza H3 virus. 

- The sample was sent to the National Influenza Center (NIC) of the Adolfo Lutz Institute, where the A(H3N2)v was confirmed by molecular tests and genomic sequencing. 

- The sequences were entered into GISAID on 1 October. 

- The sample was also shared with the WHO Collaborating Centre at the US Centers for Disease Control and Prevention (CDC), where it was genomically and antigenically characterized. 

- An epidemiological investigation was conducted, which identified the case as a student at an agricultural school where pigs and laying hens are raised, although the institution's coordinators reported that the students had not had direct contact with pigs recently. 

- It was reported that the case had contact with classmates who presented ILI symptoms during this period. 

- All household contacts were vaccinated against seasonal influenza in the 2025 season, except for the patient's mother. 

- To date, no other human cases of infection with the A(H3N2)v virus have been detected in association with this case. 

-- 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.  

For more information on zoonotic influenza viruses, see the report from the WHO Consultation on the Composition of Influenza Virus Vaccines for Use in the 2026-2027 Northern Hemisphere Influenza Season that was held on 23-26 February 2026 at this link.  

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.{11} 

- 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).{12,13} 

- State Parties to the IHR (2005) are required to immediately notify WHO of any laboratory-confirmed{14} case of a recent human infection caused by an influenza A virus with the potential to cause a pandemic{15}. 

- 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 basis16 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 risk elements. 

- The results of TIPRA complement those of the risk assessment provided here, and those of prior TIPRA risk assessments are published at  http://www.who.int/teams/global-influenza-programme/avianinfluenza/tool-for-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/ 

- WOAH/FAO Network of Expertise on Animal Influenza (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 four diseases requiring notification in all circumstances under the International Health Regulations (2005). Available at: https://www.who.int/publications/m/item/case-definitions-for-the-four-diseases-requiring-notification-towho-in-all-circumstances-under-the-ihr-(2005).  

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

{8} 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. 

{9} World Organisation for Animal Health. WAHIS. https://wahis.woah.org/#/in-review/7409. 

{10} World Health Organization. World Health Organization (10 April 2026). Disease Outbreak News: Avian Influenza A(H9N2) in Italy (https://www/who.int/emergencies/disease-outbreak-news/item/2026-DON597). 

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

{12} World Health Organization. International Health Regulations (2005), as amended through resolutions WHA67.13 (2014), WHA75.12 (2022), and WHA77.17 (2024) (https://apps.who.int/gb/bd/pdf_files/IHR_20142022-2024-en.pdf). 

{13} World Health Organization. Case definitions for the four diseases requiring notification in all circumstances under the International Health Regulations (2005) (https://www.who.int/publications/m/item/casedefinitions-for-the-four-diseases-requiring-notification-to-who-in-all-circumstances-under-the-ihr-(2005)). 

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

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

{16} World Health Organization. Operational guidance on sharing influenza viruses with human pandemic potential (IVPP) under the Pandemic Influenza Preparedness (PIP) Framework (2017) (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--31-march-2026

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