#Taiwan, Seasonal #Influenza and #COVID19 #Epidemics - Weekly Situation #Update (CDC, Oct. 6 '26): #H1N1pdm09 flu virus & #SARS-CoV-2 PQ.16.1.1 predominate

 

{Excerpt}

(...)

    According to CDC monitoring data, the domestic influenza epidemic remains stable and is still in its epidemic period. 

    In week 39 (September 27 - October 3), there were 139,060 outpatient and emergency room visits for influenza-like illnesses, a slight decrease of 1.4% from the previous week. 

    Last week (September 29 - October 5), there were 219 new cases of severe influenza complications (210 H1N1, 1 H3N2, 7 unidentified A cases, and 1 B case) and 44 deaths (41 H1N1, 1 H3N2, and 2 unidentified A cases). 

    Laboratory surveillance data shows that the influenza virus currently circulating in the community is predominantly type A, with type A H1N1 accounting for 90.7%. 

    This flu season (2025-2026) saw a total of 30 severe cases (all H1N1); the previous flu season (2024-2025) saw a total of 1,862 severe cases (1,225 H1N1, 511 H3N2, 35 unidentified A cases, and 91 B cases) and 378 deaths (247 H1N1, 107 H3N2, 12 unidentified A cases, and 12 B cases). 

    Among the severe cases, the majority were elderly people over 65 years old (66.4%) and those with a history of chronic diseases (83.6%), and 67.2% had not received the flu vaccine for this season. 

    Regarding the COVID-19 pandemic, the number of COVID-19 cases in the country has declined, but it is still in the epidemic period. 

    In the 39th week (September 27 - October 3), there were 7,836 outpatient and emergency visits for COVID-19, a decrease of 26.7% compared with the previous 7 days (September 24 - September 30). 

    Last week (September 29 - October 5), there were 37 new local severe cases and 16 local deaths. 

    This quarter (October 1, 2026 - September 30, 2027) saw a cumulative total of 12 local severe cases, with no deaths. 

    In the previous quarter (October 1, 2025 - September 30, 2026), there were a cumulative total of 781 local cases of COVID-19 complicated with severe illness, of which 163 died. 

    The majority of severe cases were among the elderly aged 65 and above (73.6%) and those with a history of chronic diseases (83.0%). 83.9% of these cases had not received the COVID-19 vaccine that quarter. In the past four weeks, the most common local case variants were PQ.16.1.1 and NB.1.8.1.

(...)

Source: 

Link: https://www.cdc.gov.tw/Bulletin/Detail/tC7VIc05_kkg8wOlIPpQIw?typeid=9

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Increased circulation of #influenza #H1N1pdm09 viruses with reduced susceptibility to #oseltamivir, #Germany 2024–2026

 

Highlights

    • The National Influenza Center for Germany (Germany NIC) detected an increase in the prevalence of A(H1N1)pdm09 viruses carrying the neuraminidase substitution NA-S247N, rising from 1.16% circulating in the 2024/25 influenza season to 56.8% in the 2025/26 season.

    • The NA-S247N substitution reduced oseltamivir susceptibility slightly; combined NA-S247N/NA-I223V/T substitutions showed reduced inhibition according WHO criteria.

    • Continuous molecular and phenotypic surveillance is essential for public health and the early detection of viruses with reduced susceptibility to antiviral drugs.

    • Rapid pyrosequencing supports the routine surveillance of neuraminidase substitutions associated with reduced susceptibility to antivirals.

    • The findings illustrate the Germany NIC's 30-year contribution to antiviral susceptibility monitoring.

Abstract

Background

Oseltamivir is still considered to be the first-line antiviral treatment for severe seasonal influenza. However, resistance to neuraminidase (NA) inhibitors poses significant challenges to influenza management. Since the 2023/24 season, A(H1N1)pdm09 viruses carrying neuraminidase substitutions (NA-I223V and/or NA-S247N) have emerged in Germany, other EU/EEA countries, and some of the World Health Organization (WHO) regions. These viruses have been linked to reduced oseltamivir susceptibility.

Methods

A rapid RT-PCR/pyrosequencing assay was developed and validated to detect NA-I223X and NA-S247X substitutions. Subsequently, a total of 765 A(H1N1)pdm09 viruses detected in Germany during the 2024/25 and 2025/26 influenza seasons were characterized phenotypically using fluorometric NA inhibition testing and/or genotypically using next-generation sequencing and pyrosequencing.

Results

The prevalence of A(H1N1)pdm09 viruses bearing the NA-S247N substitution increased from 1.2% in the 2024/25 season to 56.8% in the 2025/26 season, accounting for up to 80% of analyzed viruses by March 2026. Viruses carrying NA-S247N exhibited higher oseltamivir IC50 values than wild-type viruses. Combinations of NA-S247N with substitutions at position 223 demonstrated an additional increase. In viruses carrying the combined NA-S247N and NA-I223V/T substitutions oseltamivir showed reduced inhibition with increased IC50 values of up to 17-fold compared to wild type viruses.

Conclusions

The accumulation of NA substitutions in A(H1N1)pdm09 influenza viruses, particularly NA-S247N in combination with NA-I223V/T, substantially reduces susceptibility to oseltamivir. The marked increase in NA-S247N prevalence suggests that this substitution is becoming persistent rather than transient. Targeted pyrosequencing is a practical tool for the early detection of emerging resistance-associated substitutions.

Source: 

Link: https://doi.org/10.1016/j.ijmm.2026.151745

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Substitutions affecting the HA–NA– #receptor #balance preceded the emergence of the #pandemic 2009 #H1N1 virus

 

Abstract

Swine are a crucial species in influenza A virus (IAV) ecology, capable of supporting replication and consequently evolution of human, avian, and swine strains. They are also the source of the 2009 pandemic H1N1 virus (H1N1pdm09). Understanding how swine IAV breach the species barrier is essential for detection of potentially pandemic viruses, but is often overlooked compared to avian IAV. We hypothesize that the HA–NA balance of (pre)pandemic swine viruses is a key feature that needs adjustment as swine and humans differ in their sialoglycome. We focused on a set of (pre)pandemic swine viruses collected in Mexico following the H1N1pdm09 emergence. Phylogenetic analysis showed that the emergence was preceded by substitutions in HA and NA predicted to affect their function. Thus, HA acquired substitution A227E, previously shown to reduce receptor binding in H1N1pdm09, while NA obtained substitution S369N in the 2nd sialic acid binding site (2SBS) predicted to reduce NA cleavage. The substitutions’ effect on the HA–NA balance, was confirmed with biolayer interferometry using recombinant proteins attached to nanoparticles. Engineering recombinant attenuated influenza viruses with swine HA and NA with/without the mentioned substitutions, showed that the 2SBS substitution negatively affected replication in primary human and swine cultures. Interestingly, replication was restored by the HA substitution. Overall, we show that the emergence of H1N1pdm09 in humans was preceded by substitutions in HA and NA that were acquired in swine and adjusted the HA–NA balance. We hypothesize that adjustment of the HA–NA balance was a critical step for crossing the host–species barrier.

Source: 

Link: https://doi.org/10.1073/pnas.2609870123

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#Taiwan, Seasonal #Influenza and #COVID19 #Epidemics Weekly #Report (CDC, Sept. 29 '26): #H1N1pdm09 flu virus and #SARS-CoV-2 PQ.16.1.1 variant predominated

 

{Excerpts}

(...)

    According to data from the Taiwan Centers for Disease Control (CDC), the influenza epidemic in Taiwan remains stable and is still in its prevalent period. 

    In week 38 (September 20-26), there were 138,654 outpatient and emergency room visits for influenza-like illnesses, a slight decrease of 3.2% compared to the previous week, mainly due to outpatient closures during the long weekend. 

    Additionally, last week (September 22-28), there were 87 new severe cases of influenza (80 H1N1, 1 H3N2, and 6 untyped A cases) and 30 deaths (all H1N1). 

    Laboratory surveillance data shows that the influenza virus currently circulating in the community is predominantly type A, with type A H1N1 accounting for 87.7%. 

    This flu season (2015-2016) saw a cumulative total of 1,673 severe cases (1,041 H1N1, 510 H3N2, 32 unclassified H1N1, and 90 H1N1) and 334 deaths (206 H1N1, 106 H3N2, 10 unclassified H1N1, and 12 H1N1). 

    The majority of severe cases were among those aged 65 and above (65.9%) and those with a history of chronic illnesses (83.4%). 67.7% of patients had not received the flu vaccine this season. 

    Regarding the COVID-19 pandemic, while the number of cases in Taiwan has decreased, it remains in an epidemic period. 

    In week 38 (September 20-26), there were 10,502 outpatient and emergency room visits related to COVID-19, a 28.4% decrease compared to the previous week (September 13-19). 

    Last week (September 22-28), there were 33 new severe cases and 14 new deaths. 

    Since October 2025, there have been a total of 756 cases of COVID-19 complicated by severe illness, of which 147 have died. 

    The majority of severe cases are among the elderly aged 65 and above (73.7%) and those with a history of chronic diseases (82.9%). 83.6% of these cases have not received the COVID-19 vaccine this season. 

    In the past four weeks, the most prevalent local case variants have been PQ.16.1.1 and NB.1.8.1.

(...)

Source: 

Link: https://www.cdc.gov.tw/Bulletin/Detail/PkxM8mKEAbKUXcS81xFuxQ?typeid=9

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#Recommendations announced for #influenza #vaccine composition for the 2027 southern hemisphere influenza season (WHO, extract)

 

{Excerpts}

(...)

    From February to August 2026, influenza A(H1N1)pdm09, A(H3N2) and influenza B viruses circulated in varying proportions across all regions of the world, causing disease. 

    Influenza A viruses were the most common in most regions, except Northern and Western Africa, North America and Eastern Asia, where influenza B viruses dominated.

    WHO recommends that vaccines for use in the 2027 southern hemisphere influenza season contain 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.

    As part of the review, experts also looked at influenza viruses circulating in animals, particularly those that have caused infections in humans. These animal or zoonotic influenza viruses remain a significant concern because of their potential to cause pandemics.

(...)

Source: 

Link: https://www.who.int/news/item/25-09-2026-recommendations-announced-for-influenza-vaccine-composition-for-the-2027-southern-hemisphere-influenza-season

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Molecular #Epidemiology and #Evolution of Swine #Influenza A Viruses, #Vietnam, 2020–2024

 

Abstract

Swine influenza A viruses (IAV-S) caused the 2009 H1N1 pandemic and pose a future zoonotic and pandemic threat. Vietnam represents a critical hotspot for IAV-S emergence within East and Southeast Asia, with dense swine and human populations and intensive livestock trade. We conducted genomic surveillance of IAV-S in Vietnam during 2020–2024, extending previous surveillance from 2013–2019. We identified multiple co-circulating H1 and H3 clades, including pandemic H1N1, Eurasian avian-like, and European lineages, by conducting phylogenetic analysis of 56 IAV-S isolates (21 H1N1, 31 H1N2, and 4 H3N2). Three H1 clades persisted exclusively in Vietnam, circulating up to 12 years. Phylogeographic analysis revealed multiple independent introduction events from North America, Europe, China, Thailand, and Cambodia. We detected extensive reassortment that frequently involved pandemic H1N1 virus internal genes. We identified several lineage-specific mutations associated with mammalian adaptation. Our findings underscore the ongoing IAV-S evolution and need for sustained surveillance in Vietnam.

Source: 

Link: https://doi.org/10.3201/eid3210.260593

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#Taiwan, Seasonal #Influenza and #COVID19 Epidemics Weekly Report (CDC, Sept. 22 '26): #H1N1pdm09 & #SARS-CoV-2 PQ.16.1.1 viruses predominated

 

{Excerpt}

(...)

    The CDC noted that the influenza epidemic in Taiwan is slightly rising and in its epidemic season. 

    In week 37 (September 13-19), there were 141,375 outpatient and emergency room visits for influenza-like illnesses, a slight increase of 1.4% compared to the previous week. 

    Additionally, last week (September 15-21), there were 165 new cases of severe influenza complications (151 H1N1, 6 H3N2, and 8 untyped A cases) and 30 deaths (27 H1N1, 2 H3N2, and 1 untyped A case). 

    Laboratory monitoring data shows that the influenza virus currently circulating in the community is mainly type A, with type A H1N1 accounting for 84.9% of the cases. 

    This influenza season (2025-2026) saw a cumulative total of 1,586 severe cases (958 H1N1, 509 H3N2, 29 untyped type A, 90 type B) and 304 deaths (176 H1N1, 106 H3N2, 10 untyped type A, 12 type B). 

    Severe cases were predominantly among those aged 65 and above (65.8%) and those with a history of chronic diseases (83.2%). 67.8% of patients had not received the influenza vaccine this season.

    According to data from the Taiwan Centers for Disease Control (CDC), the COVID-19 epidemic in Taiwan is declining, but it is still in its epidemic period. 

    In the 37th week (September 13-19), there were 14,462 outpatient and emergency room visits related to COVID-19, a 20.6% decrease compared to the previous week (September 6-12). 

    Last week (September 15-21), there were 48 new severe cases and 9 new deaths. 

    Since October 2025, there have been a cumulative total of 723 cases of COVID-19 complicated by severe illness, of which 133 have died. 

    The majority of severe cases are among those aged 65 and above (73.3%) and those with a history of chronic diseases (82.6%). 83.8% of these cases have not received the COVID-19 vaccine this season. 

    In the past four weeks, the most prevalent local variants in cases have been NB.1.8.1 and PQ.16.1.1.

(...)

Source: 

Link: https://www.cdc.gov.tw/Bulletin/Detail/Tj9G4dJj3yMmEE0URl49CA?typeid=9

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Near real-time data on the #human neutralizing #antibody #landscape to #influenza virus in summer of 2026 shows antigenic advance of #H3N2 subclade K region D mutants and #H1N1 D.3.1.1 Sa mutants

 

Abstract

Human seasonal influenza evolves rapidly, necessitating twice yearly decisions about whether to update the strains in the vaccine. To help inform this decision, we have been using high-throughput sequencing-based neutralization assays to make twice yearly measurements of how recent human sera neutralize current human H3N2 and H1N1 strains. Here we provide the third installment in this series of measurements by reporting 47,851 titers representing neutralization of 148 viral strains by 325 human sera collected between April and August of 2026. Our measurements show that new H3N2 subclade K strains with mutations in antigenic region D and new H1N1 subclade D.3.1.1 strains with mutations in antigenic region Sa (such as G155E) have reduced neutralization by human sera, with notable heterogeneity in the impact of some of these mutations across sera from different individuals. This paper is accompanied by an interactive summary (https://jbloomlab.github.io/flu-seqneut-2026/summary.html) that enables detailed exploration of the results, and all titer data are publicly available for further analysis to aid vaccine antigen selection and studies of viral evolution.

Competing Interest Statement

JDB consults for Pfizer, GSK, Apriori Bio, and Merck. JDB has received stock options in the Vaccine Company. JDB is an inventor on Fred Hutch licensed patents related to techniques to characterize the antigenic effects of viral variation. SEH is a co-inventor on patents that describe the use of nucleoside-modified mRNA as a vaccine platform. SEH reports receiving consulting fees from Sanofi, Pfizer, Lumen, Novavax, and Merck. ALG reports contract testing to UW from Abbott, Cepheid, Novavax, Pfizer, Janssen, Assembly Biosciences, Aicuris, Innovative Molecules, and Hologic, research support from Gilead, personal consulting fees from Arisan Therapeutics, outside of the described work. JAE reports support to her institution from GSK, Pfizer, Moderna, and is a consultant for GSK, Pfizer, Merck, Meissa vaccines, Moderna, and Shionogi. ST reports research funding from Pfizer for a separate study.

Funder Information Declared

National Institute of Allergy and Infectious Diseases, R01AI165821, F30AI186284, 75N93021C00015

Howard Hughes Medical Institute, https://ror.org/006w34k90

Source: 

Link: https://doi.org/10.64898/2026.09.15.751855

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#Taiwan, Seasonal #Influenza and #COVID19 #Epidemics Weekly #Update (CDC, September 15 '26): #H1N1pdm09 flu virus & #SARS-CoV-2 PQ.16.1.1 predominated

 

{Excerpts}

(...)

    The CDC pointed out that the domestic influenza epidemic is rising and in its epidemic season. 

    In the 36th week (September 6th-12th), there were 136,796 outpatient and emergency room visits for influenza-like illnesses, an increase of 16.5% compared to the previous week. 

    Additionally, last week (September 8th-14th), there were 92 new cases of severe influenza complications (79 H1N1, 5 H3N2, and 8 untyped A cases) and 21 deaths (18 H1N1, 2 H3N2, and 1 untyped A case). 

    Laboratory monitoring data shows that the influenza virus currently circulating in the community is mainly type A, with type A H1N1 accounting for 82.2%. 

    This flu season has seen a cumulative total of 1,421 severe cases (800 H1N1, 503 H3N2, 28 untyped type A, and 90 type B) and 274 deaths (149 H1N1, 104 H3N2, 9 untyped type A, and 12 type B). 

    The majority of severe cases are among those aged 65 and above (65.0%) and those with a history of chronic diseases (82.7%). 68.3% of those affected have not received the flu vaccine this season.

    According to data from the Taiwan Centers for Disease Control (CDC), the COVID-19 epidemic in Taiwan is declining, but it is still in its epidemic period. 

    In week 36 (September 6-12), there were 17,847 outpatient and emergency room visits related to COVID-19, a 13.3% decrease compared to the previous week (August 30-September 5). 

    Last week (September 8-14), there were 53 new severe cases and 18 local deaths. 

    Since October 2025, there have been a cumulative total of 675 locally transmitted cases of COVID-19 complicated by severe illness, of which 124 have died. 

    Severe cases are predominantly among those aged 65 and above (73.3%) and those with a history of chronic diseases (82.8%). 83.6% of these cases have not received the COVID-19 vaccine this season. 

    In the past four weeks, the most prevalent local variants have been NB.1.8.1 and PQ.16.1.1.

(...)

Source: 

Link: https://www.cdc.gov.tw/Bulletin/Detail/CqW5UAMFqpDkwJWfWG-WGw?typeid=9

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Emergence and spread of NA-I223V and NA-S247N double-mutant #H1N1pdm09 #influenza viruses with reduced #oseltamivir susceptibility in the #Netherlands and beyond, 2023 to 2026

 

Abstract

In 2023/24, A(H1N1)pdm09 influenza viruses with neuraminidase (NA)-S247N emerged in NA-clade C.5.3.3 carrying NA-I223V, spread internationally, then faded. Such double mutants reappeared sporadically in 2024/25. They expanded again in 2025/26 in NA-clade D.3 viruses carrying NA-S247N after acquiring NA-I223V in Europe – notably Spain, the Netherlands, Finland and France, and beyond. Dutch double mutants from both seasons showed median 12- and 13-fold reduced inhibition by oseltamivir. These findings underscore the need for ongoing genomic and phenotypic monitoring of antiviral susceptibility.

© Creative Commons License. This work is licensed under a Creative Commons Attribution 4.0 International License.

Source: 

Link: https://doi.org/10.2807/1560-7917.ES.2026.31.36.2600733

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Updated #H1N1pdm09 #influenza virus #ferret infection #model permits refined #antiviral #assessment using aerosol inhalation challenge

 

Abstract

Seasonal influenza viruses continue to pose a significant threat to human health. As influenza viruses exhibit sustained genetic drift, it is imperative that animal studies utilize challenge strains that reflect contemporary, currently circulating viruses when evaluating pathogenicity, viral tropism, transmissibility, and antiviral sensitivity to better inform public health responses. Ferrets are considered the gold-standard small animal model for assessing currently circulating influenza viruses. Seasonal influenza A(H1N1)pdm09 viruses replicate well in both the upper and lower respiratory tract of ferrets, providing an important model for developing improved vaccination and therapeutic strategies; however, many of these studies have relied on a 2009 virus isolate. Utilising representative influenza A(H1N1)pdm09 virus strains from 2009 to 2022, we explored virus replication kinetics and lung pathogenesis in ferrets following intranasal inoculation with these contemporary strains. Our results revealed strain specific differences, with greater lung viral loads and pathogenesis following inoculation with A/Sydney/5/2021 compared to other strains. Efficient transmissibility of A/Sydney/5/2021 virus to naïve recipients was also observed following both contact and airborne exposure to infected donor ferrets. To refine this updated model, we performed side-by-side evaluation of oseltamivir antiviral efficacy following traditional intranasal or aerosol inhalation influenza challenges. Pre-treatment with oseltamivir demonstrated greater reductions in viral shedding from the upper respiratory tract than post-infection treatment of ferrets infected by aerosol inhalation, while the intranasal route showed reduced oseltamivir efficacy independent of the timing of antiviral treatment. These findings provide the basis for using an updated A(H1N1)pdm09 challenge virus for ferret studies as an alternative to the commonly used, but now less relevant 2009 early pandemic viruses. It also highlights how different methods of virus inoculation can influence outcomes of ferret antiviral studies, with an aerosol challenge model able to demonstrate differences between therapeutic and prophylactic treatments, which were not apparent with an intranasal challenge model.

Source: 

Link: https://journals.plos.org/plospathogens/article?id=10.1371/journal.ppat.1014604

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#Taiwan, Seasonal #Influenza and #COVID19 Epidemics Weekly #Update (CDC, September 8 '26): H1N1pdm09 flu virus & SARS-CoV-2 PQ.16.1.1 variant are predominant

 

{Excerpts}

(...)

    The CDC pointed out that in week 35 (August 30th - September 5th), there were 115,136 outpatient and emergency room visits for influenza-like illnesses, an increase of 11.0% from the previous week, showing a recent upward trend. 

    The percentage of emergency room visits reached 11.2%, exceeding the epidemic threshold (11.0%), indicating the start of the epidemic period. 

    Additionally, last week (September 1st - September 7th), there were 105 new cases of severe influenza complications (97 H1N1, 4 H3N2, 4 untyped A cases) and 19 deaths (18 H1N1, 1 untyped A case). 

    Laboratory monitoring data shows that the influenza virus currently circulating in the community is mainly type A, with type A H1N1 accounting for 79.4% of the cases. 

    This flu season (2023-2024) has seen a cumulative total of 1,329 severe cases (717 H1N1, 498 H3N2, 24 untyped type A, and 90 type B) and 253 deaths (131 H1N1, 102 H3N2, 8 untyped type A, and 12 type B). 

    The majority of severe cases are among those aged 65 and above (65.1%) and those with a history of chronic diseases (82.8%). 68.6% of those affected have not received the flu vaccine this season.

    According to data from the Taiwan Centers for Disease Control (CDC), the COVID-19 epidemic in Taiwan is declining, but it is still in its epidemic period. 

    In week 35 (August 30 - September 5), there were 20,199 outpatient and emergency room visits related to COVID-19, a 9.7% decrease compared to the previous week (August 23 - August 29). 

    Last week (September 1 - September 7), there were 73 new severe cases and 15 deaths. 

    Since October 2025, there have been a cumulative total of 622 locally transmitted cases of COVID-19 complicated by severe illness, of which 106 have died. 

    The majority of severe cases are among those aged 65 and above (72.7%) and those with a history of chronic diseases (83.0%). 84.9% of these cases have not received the COVID-19 vaccine this season. 

    In the past four weeks, the predominant variant strain in locally transmitted cases has been PQ.16.1.1.

(...)

Source: 

Link: https://www.cdc.gov.tw/Bulletin/Detail/5gJTj70wu9L3psY5kQLUuA?typeid=9

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#Report on #influenza viruses received and tested by the #Melbourne #WHO Collaborating Centre for Reference and Research on Influenza during 2025

 

Abstract

As part of its role in the World Health Organization (WHO) Global Influenza Surveillance and Response System (GISRS), the WHO Collaborating Centre for Reference and Research on Influenza in Melbourne (the Centre) received 13,817 human influenza-positive samples during 2025. Viruses were analysed for their antigenic, genetic, and antiviral susceptibility properties. Selected viruses were propagated in qualified cells or embryonated hens’ eggs for potential use in seasonal influenza virus vaccines. Of the 13,817 samples received or processed, influenza A(H1N1)pdm09 viruses predominated, accounting for 46.1% of samples, compared to 21.2% for A(H3N2) viruses and 19.5% for influenza B viruses; one influenza C virus was received. Among viruses analysed at the Centre, the majority of A(H1N1)pdm09 (> 99%) and influenza B (98%) viruses were antigenically similar to their respective WHO recommended vaccine strains for the Southern Hemisphere in 2025. In contrast, only 43% of A(H3N2) viruses were antigenically similar to their respective WHO recommended vaccine strains. Of 3,307 samples tested for susceptibility to the neuraminidase inhibitors oseltamivir and zanamivir, 37 A(H1N1)pdm09 viruses showed highly reduced inhibition by oseltamivir and no influenza viruses tested showed highly reduced inhibition by zanamivir. Of 5,080 samples with sequencing of the polymerase acidic (PA) gene, no genetic markers associated with highly reduced susceptibility to baloxavir marboxil were identified.

Source: 

Link: https://ojs.cdi.cdc.gov.au/index.php/cdi/article/view/3489

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#Taiwan, Seasonal #Influenza and #COVID19 Epidemics Situation #Update (CDC, September 1 '26): #H1N1pdm09 flu virus and PQ.16.1.1 SARS-CoV variant are predominant

 

{Excerpt}

(...)

    The CDC pointed out that in the 34th week (August 23-29), there were 101,628 outpatient and emergency room visits for influenza-like illnesses, an increase of 5.6% compared to the previous week, showing a recent slow upward trend. 

    In addition, last week (August 25-31), there were 85 new cases of severe influenza complications (80 H1N1, 3 H3N2, and 2 untyped A cases) and 14 deaths (12 H1N1, 1 H3N2, and 1 untyped A case). 

    Laboratory monitoring data shows that the influenza virus currently circulating in the community is mainly type A, with type A H1N1 accounting for 74.1% of the cases. 

    This flu season (2023-2024) has seen a cumulative total of 1,224 severe cases (620 H1N1, 494 H3N2, 20 untyped type A, and 90 type B) and 234 deaths (113 H1N1, 102 H3N2, 7 untyped type A, and 12 type B). 

    The majority of severe cases are among those aged 65 and above (64.6%) and those with a history of chronic diseases (82.8%). 69.4% of those affected have not received the flu vaccine this season.

    According to data from the Taiwan Centers for Disease Control (CDC), the COVID-19 epidemic in Taiwan is declining, but it remains at a plateau. 

    In the 34th week (August 23-29), there were 21,969 outpatient and emergency room visits related to COVID-19, a 13.4% decrease compared to the previous week (August 16-22). 

    Last week (August 25-31), there were 69 new locally transmitted severe cases and 18 local deaths. 

    Since October 2025, there have been a cumulative total of 549 locally transmitted cases of COVID-19 complicated by severe illness, of which 91 have died. 

    The majority of severe cases are among those aged 65 and above (72.5%) and those with a history of chronic diseases (83.1%). 85.1% of these cases have not received the COVID-19 vaccine this season. 

    In the past four weeks, the predominant variant strain in locally transmitted cases has been PQ.16.1.1.

(...)

Source: 

Link: https://www.cdc.gov.tw/Bulletin/Detail/GWRkQ03fZuKKWwdv191UyQ?typeid=9

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#Antibody profiles across #H5N1 and previously circulating viruses are highly dynamic and #age- and imprint- independent

 

Abstract

The increasing incidence of H5N1 influenza virus transmission from animal species to humans has heightened concerns about an imminent H5N1 pandemic. Prior studies using recombinant hemagglutinin and neuraminidase proteins have reported age-dependent cross-reactivity to H5N1, attributed to immune imprinting from an individual's first influenza virus exposure. However, whether this pattern holds when using whole inactivated virus (WIV), capturing antibodies against diverse viral proteins, and is stable over time remains unknown. We therefore aimed to determine whether H5N1 cross-reactivity of pre-existing antibodies to whole virus follows an age-dependent or imprinting-specific pattern, and whether this pattern is stable over a five-year period. To this end, we measured serum antibody levels in adolescents, adults and seniors by ELISA using whole inactivated H5N1 virus as antigen rather than purified proteins. Detectable, albeit generally low, levels of H5N1-reactive antibodies were present in most individuals, irrespective of age. Comparison of antibody levels against H5N1 with those to five historical influenza virus strains revealed a consistent positive correlation between H5N1-reactive antibodies and responses to the H1N1pdm09 strain A/California/7/2009 (CA), across all age groups. Using unbiased clustering of antibody titers against H5N1, CA, and the H3N2 strain A/Perth/16/2009 (PE), we identified seven distinct age-transcending antibody profiles. These profiles covered individuals with varying titers to all three included viruses but also identified individuals with high anti-CA levels, yet low anti-H5N1 levels and vice versa. Moreover, despite stable antibody levels over a five-year interval in the study population, individual antibody levels and profiles fluctuated considerably over this period. Taken together, our results confirm the presence of H5N1-reactive antibodies in human sera and their association with previously circulating strains. However, they also caution against inferring antibody levels against a new strain based solely on responses to antigenically related strains and highlight the limitations of extrapolating immune status from single timepoint measurements.

Competing Interest Statement

The authors have declared no competing interest.

Source: 

Link: https://www.medrxiv.org/content/10.64898/2026.08.26.26361396v1

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#Influenza A virus #H5N1 genotypes #B3.13 and D1.1 show #temperature-dependent restriction of #replication in primary #human respiratory epithelial cell cultures derived from the upper and lower respiratory tract

 

Abstract

H5N1 clade 2.3.4.4b avian influenza A viruses pose a significant threat to wild animal populations, domesticated animals, and potentially, the human population. For H5N1s to infect and transmit among mammalian species, mutations for improved utilization of mammalian receptors and enhanced replication at the lower temperatures of the upper respiratory tract need to be acquired. A human H1N1pdm09-like virus was compared to H5N1 genotypes B3.13 and D1.1 for replication at 33ºC, 37ºC, and 39ºC – temperatures consistent with the upper and lower respiratory tract in humans, and dairy cow udder tissue. All H5N1 viruses had increased plaque sizes on MDCK cells at 37ºC and 39ºC compared to H1N1pdm09. In primary, differentiated human nasal and bronchial epithelial cultures, all H5N1 viruses show restricted infectious virus production compared to H1N1 at 33ºC. While H5N1 D1.1 also showed restricted replication at 37ºC and 39ºC, the H5N1 B3.13 replicated to nearly equivalent titers as H1N1pdm09. All H5N1 viruses demonstrated similar cell tropism in cells from the upper and lower respiratory tract, infecting more ciliated than non-ciliated cells relative to H1N1pdm09. H1N1, H5N1 B3.13 D1.1 infection induced similar innate immune factors, with nasal epithelial cells producing higher levels compared to bronchial epithelial cells. These data suggest that genotype B3.13 and D1.1 H5N1 viruses show different temperature dependent replication patterns compared to H1N1pdm09.

Source: 

Link: https://www.biorxiv.org/content/10.64898/2026.08.27.747488v1

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#Global Respiratory #Virus #Activity: Weekly #Update (WHO, August 28 '26)

 

{Excerpt, from Weekly Epidemiological Record}

(...)

    The findings below are based on surveillance conducted through the WHO Global Influenza Surveillance and Response System (GISRS). 

    More details can be found on the Global Influenza Programme's surveillance and monitoring page.

Overview

    ° In week 33 2026, influenza positivity was below 10% and SARS-CoV-2 activity remained low globally. 

    ° During the past few weeks, influenza positivity remained just below 10% overall in the tropical areas and southern hemisphere temperate and subtropical areas. 

    ° RSV positivity also remained low globally.

Influenza

    ° Globally, influenza detections remained low in week 33 with influenza A and B viruses detected in similar proportions.

    ° In the southern hemisphere, influenza percent positivity was elevated (>10%) in one country in Temperate South America. 

    ° Percent positivity was over 30% in one country in Oceania where a medium increase in activity was observed.

    ° In the northern hemisphere, influenza percent positivity was elevated (>10%) in some countries in Central America and the Caribbean, Tropical South America, Western Africa, Western, Southern and South-East Asia and in single countries in Middle Africa, South West and Northern Europe and Eastern Asia. 

    ° Percent positivity was over 30% in single countries in Tropical South America, Western and Eastern Africa and Southern Asia. 

    ° Increases in activity were observed in some countries in Central America and the Caribbean and Southern Asia and in single countries in Tropical South America, Western, Eastern and Middle Africa, South West Europe and Western Asia.

    ° In the zones with elevated positivity, influenza A(H3N2) was predominant in South West Europe, Eastern Africa, Eastern Asia and Oceania; influenza A(H1N1)pdm09 was predominant in Western, Southern and South-East Asia and influenza B was predominant in Tropical and Temperate South America. 

    ° Influenza A and B were codominant in Central America and the Caribbean and Western Africa and influenza A(H1N1)pdm09 and influenza A(H3N2) were codominant in Middle Africa.

SARS-CoV-2

    ° Globally, SARS-CoV-2 positivity remained stable and low across most reporting countries, with elevated positivity (>10%) reported in countries in Central America and the Caribbean and in single countries in Tropical South America, Southern and South-East Asia. 

    ° Small increases in activity were observed in countries in Central America and the Caribbean, Northern Europe and in a single country in Southern Asia.

Respiratory Syncytial Virus (RSV)

    ° RSV positivity was elevated (>10%) in a few countries in Central America and the Caribbean, Tropical and Temperate South America and in a single country in Southern Asia. 

    ° Percent positivity was over 30% in a single country in Temperate South America. 

    ° Small increases in activity were observed in two countries in Central America and the Caribbean. 

    ° RSV and influenza activity were both elevated in single countries in Temperate South America and Southern Asia.

Severity assessment

    ° The severity assessments here are reported from countries, areas and territories. 

    ° Assessments for transmissibility can be reported based on syndromic parameters and/or influenza-specific parameters. 

    ° In the southern hemisphere temperate and subtropical areas, influenza-specific transmissibility was reported as low (1) and moderate (1); transmissibility using syndromic data was reported as moderate (1). 

    ° In the northern hemisphere temperate and subtropical areas, influenza-specific transmissibility was reported as below seasonal threshold (11) and low (2); transmissibility using syndromic data was reported as below seasonal threshold (8). 

    ° Influenza-specific transmissibility was reported as moderate in one country in the tropical areas.

Current update: Global Respiratory Virus Activity: Weekly Update N° 592

All past updates: Global respiratory virus updates

(...)

Source: 

Link: https://www.who.int/publications/journals/weekly-epidemiological-record/wer101-34

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#Taiwan, #Epidemics of Respiratory Viruses (#COVID19, #Influenza, #Enteroviruses) Weekly Update (CDC, August 25 '26): PQ.16.1.1 Variant Still Predominant

 

{Excerpts}

(...)

    CDC monitoring data shows that the domestic COVID-19 epidemic is at a plateau. 

    In week 33 (August 16-22), there were 24,995 outpatient and emergency room visits for COVID-19, a 6.0% decrease compared to the previous week (August 9-15). 

    Last week (August 18-24), there were 59 new locally transmitted severe cases and 19 new locally transmitted deaths. 

    Since October 2025, there have been a total of 480 local cases of COVID-19 complicated by severe illness, of which 73 have died. 

    The majority of severe cases are among those aged 65 and above (73.5%) and those with a history of chronic diseases (82.5%). 86.5% of these cases have not been vaccinated this season. 

    In the past four weeks, the predominant variant strain in local cases has been PQ.16.1.1.     

    As of August 24, approximately 1.823 million doses of the COVID-19 vaccine have been administered this season. There are currently about 111,000 doses remaining nationwide, which will be available until September 9. Eligible and needy individuals are advised to take advantage of this time and get vaccinated as soon as possible.

    Regarding the influenza epidemic, in week 33 (August 16-22), there were 94,340 outpatient and emergency room visits for influenza-like illnesses, a slight decrease of 2.5% compared to the previous week. 

    Additionally, last week (August 18-24), there were 64 new cases of severe influenza complications (59 H1N1 and 5 H3N2) and 15 deaths (all H1N1). 

    Laboratory surveillance data shows that the influenza virus currently circulating in the community is predominantly type A, with type A H1N1 accounting for a high percentage at 69.7%. 

    This flu season (2014-2015) saw a cumulative total of 1,139 severe cases (540 H1N1, 491 H3N2, 18 untyped A, and 90 B) and 220 deaths (101 H1N1, 101 H3N2, 6 untyped A, and 12 B). 

    The majority of severe cases were among those aged 65 and over (63.8%) and those with a history of chronic illness (82.4%). 71.0% of patients had not received the flu vaccine this season.

    Regarding enterovirus cases, in week 33 (August 16-22), there were 6,546 outpatient and emergency room visits, similar to the previous week (6,646), indicating a stable recent trend. 

    Laboratory surveillance over the past four weeks showed that Coxsackievirus A6 was the most prevalent enterovirus in the community, followed by enterovirus D68 and Coxsackievirus A16. 

    This year (2026), there have been a total of 6 confirmed cases of enterovirus infection complicated with severe illness (including 1 death), including 4 cases of enterovirus D68, 1 case each of Coxsackievirus A4 and Coxsackievirus A16. 

    Regarding the dengue fever outbreak, as of August 24th this year, there have been a total of 134 confirmed dengue fever cases, including 7 local cases (all residing in Kaohsiung City) and 127 imported cases. The imported cases were mainly from Southeast Asian and South Asian countries such as Indonesia (26 cases), Vietnam (26 cases), and the Maldives (16 cases). The cumulative number of cases is lower than the same period in 2025 (152 cases).

(...)

Source: 

Link: https://www.cdc.gov.tw/Bulletin/Detail/QiAsLBvifNAj7FJzGc-ApQ?typeid=9

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Detection and characterization of #antiviral #resistant viruses during the #influenza season of 2024–25

 

ABSTRACT

During the high severity season of 2024–25, CDC with public health partners sequenced and analyzed genomes of >10,000 influenza viruses for antiviral resistance markers. Available sequence-flagged and representative viruses were tested with antivirals using in vitro assays. In the US, three oseltamivir-resistant A(H3N2) viruses had treatment-emergent neuraminidase (NA) mutations, either E119V or R292K. Oseltamivir-resistant A(H1N1)pdm09 viruses with NA-H275Y were detected in 15 states, albeit at a low frequency (0.53%). They belonged to several phylogenetic groups, with hemagglutinin (HA) subclade D.3.1 combined with either NA subclade D.1 or D.2 being most common. Based on shared sequence data, nearly all H275Y viruses from Australia, Canada, and Chile also belonged to these HA and NA subclades. Conversely, most H275Y viruses (68/81) from China belonged to HA subclade C.1.9 and NA subclade D and shared the permissive mutation R257K. Influenza polymerase acidic (PA) mutations conferring 4- to 92-fold decreased baloxavir susceptibility were detected in nine influenza A viruses. Viruses with PA-I38T showed mild attenuation of replicative fitness in three cell lines. Based on available data, NA-H275Y and PA-I38T viruses were collected from patients with no exposure to antivirals. Baseline susceptibility to all US-approved influenza antivirals remained largely unchanged compared to previous seasons. All swine-origin viruses detected in the US had adamantane resistance-conferring marker, M2-S31N, but remained susceptible to other approved antivirals. Monitoring antiviral susceptibility has substantially improved with increased sequencing capacities and bioinformatic support at public health laboratories. Information gained through influenza surveillance has been used to guide recommendations on antiviral use.

Source: 

Link: https://journals.asm.org/doi/10.1128/spectrum.01514-26

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#Assessment of #influenza virus and #coronavirus #tropism, #replication competence and disease severity in ex vivo and in vitro cultures of the #human respiratory tract

ABSTRACT

The emergence of animal influenza viruses circulating in poultry and human populations poses a significant public health threat, yet current risk assessment tools that connect surveillance data to human transmission risk and disease severity are lacking. To address this, we employed a semi-quantitative approach to analyze virus tropism and replication competence, conducting risk assessments of influenza and coronavirus adaptation to human transmission in an ex vivo model, and evaluating virus-induced impairment of alveolar fluid clearance (AFC) in vitro as a correlation of disease severity. Our results showed that seasonal influenza A H1N1, H3N2, influenza B, MERS-CoV, and SARS-CoV exhibited productive viral replication and tissue infection in bronchial tissues, whereas wild bird surveillance isolates such as H5N3 and H7N1 showed minimal replication when compared to pandemic H1N1 and highly pathogenic avian influenza (HPAI) H5N1. Notably, differential lung viral replication and tissue tropism were detected for H5N6 and H9N2. HPAI H5N1, H7N9, MERS-CoV, and SARS-CoV caused more severe AFC impairment than seasonal H1N1, H3N2, and influenza B viruses, correlating with their clinical severity. Overall, these findings revealed an important association between viral tropism and human transmissibility in ex vivo explants, as well as the impairment of AFC in vitro, which aligns with the clinical manifestations of disease severity across different viral strains.

Source: 

Link: https://www.microbiologyresearch.org/content/journal/jgv/10.1099/jgv.0.002281

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