PAHO Briefing Note: Influenza A(H3N2) subclade K (J.2.4.1), considerations for the Americas Region - 11 December 2025

 

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While it remains to be seen just how impactful - or prolonged - this year's Northern Hemisphere flu season will end up being, from what we've already seen (see WHO DON: Seasonal influenza - Global situation) with this new (`drifted') subclade K H3N2 virus, we could be in for a long winter.

Late this week PAHO (the Pan American Health Organization) published a press release (below), and advice to member nations, on ways to deal with what may prove to be a difficult season. 

First the press release, followed by the update for PAHO member nations.

PAHO calls for strengthened vaccination and surveillance in the Americas amid a global increase of influenza A(H3N2) subclade K

12 Dec 2025


Washington, D.C., 12 December 2025 (PAHO/WHO) – The Pan American Health Organization (PAHO) has issued a briefing note, updating countries on the increasing circulation of the influenza A(H3N2) subclade K (J.2.4.1) virus in several regions of the world, and to reiterate the call to strengthen surveillance and promote vaccination—particularly among older adults and people with risk factors. PAHO also urges countries to ensure timely clinical management of cases and prepare health services for the possibility of early, or more intense, respiratory disease activity.

According to the latest data, circulation of subclade K has risen rapidly in Europe and several Asian countries, where it now represents a substantial proportion of detected influenza A(H3N2) viruses. Health authorities in those countries have not reported significant changes in clinical severity; however, seasons dominated by the A(H3N2) subtype have historically been associated with greater impact among older adults.

In North America, the United States and Canada are also reporting a progressive increase in detections of subclade K. To date, similar circulation has not been observed in South America, based on data reported to the Global Initiative on Sharing All Influenza Data (GISAID).

PAHO noted that the genetic evolution observed in subclade K is part of the natural variation process of seasonal influenza viruses. Although evidence on vaccine effectiveness for the current season remains limited, preliminary data from Europe indicate that vaccination continues to provide protection comparable to previous years against severe disease, including hospitalization.
Recommendations for countries

PAHO urged Member States to maintain and strengthen epidemiological, virological, and genomic surveillance; ensure high vaccination coverage; provide timely treatment of cases; and reinforce the preparedness of health services for the possibility of early or more intense activity during the 2025–2026 season in the Northern Hemisphere.

The Organization reiterated the importance of seasonal influenza vaccination for older adults, people with chronic conditions, pregnant women, and other groups at higher risk of complications, emphasizing that vaccinating these populations also helps reduce pressure on hospitalization services.

PAHO also recalled that the recommendations outlined in the December 4 Epidemiological Alert remain in effect. These include strengthening surveillance for influenza, respiratory syncytial virus (RSV), and SARS-CoV-2; ensuring continuous reporting of data; and regularly submitting samples for sequencing to detect variants that may alter virus transmissibility or severity.

The Organization further underscored the importance of early diagnosis, reinforced prevention and control measures, availability of antivirals for at-risk groups, and the immediate investigation and reporting of unusual respiratory events, in accordance with the International Health Regulations.

Personal preventive measures—such as handwashing, covering coughs and sneezes, and staying home when experiencing fever or respiratory symptoms—remain essential to limit transmission.

You'll can read the above referenced briefing note below.  I'll have a brief postscript after the break.

 

While we tend to treat the seasonal flu as primarily a serious risk to the elderly or frail, every once in a while a new flu strain will emerge that is a viral overachiever.  

Even though we are coming off one of the worst flu seasons in more than a decade (see MMWR: Influenza-Associated Hospitalizations During a High Severity Season (United States, 2024–25)), this year could prove even more challenging. 

 

Unlike last year, there are concerns over the reduced effectiveness of this year's vaccine (although it may still help prevent severe illnesses), which - along with reduced uptake of the vaccine - may leave a lot of people more susceptible. 

With flu still rising in North America, it isn't too late to get a flu shot.  I got mine in October, and am glad I did. But I'll also wear a mask in public, and use copious amounts of hand sanitizer this winter. 

Over the past 20 years we've looked at a number of `outlier' flu seasons, where hospitals got slammed, and deaths far exceeded the norm (see When Seasonal Influenza Goes Rogue).

While a novel flu virus (like H5N1, or H9N2) would likely be worse, they generally emerge only a few times each century. Seasonal flu comes around every year, and history has repeatedly shown that these viruses should not be underestimated.

Making anything you can do (vaccines, facemasks, hand sanitizer, etc.) to reduce your risks of infection, more than worth the effort.

Hawaii: State Agencies Respond to 3rd Possible Case of HPAI H5 (Kauaʻi)

Hawaii lies beneath the West Pacific Flyway

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Separated as it is by vast ocean distances - 2,400 miles to the U.S., 4,000 miles to Japan - Hawaii is considered the world's most isolated populated place on earth. 

And not surprisingly - until just over a year ago  - the state of Hawaii had never reported H5N1 in wild or domesticated birds. 

All that changed in November of 2024 after the virus was first detected in wastewater samples on Oahu, and at least two outbreaks in captive and/or wild birds the following week. 

A month later, another treatment plant on the island of Hilo reported the virus.

This year, the first reported case came in mid-October (see Hawaii: DOH, DAB, DLNR Investigate Possible Avian Flu Case in Waterfowl), followed a month later by Hawaii: State Agencies Respond to 2nd Confirmed Case of HPAI H5 (Maui).

Yesterday the State of Hawaii announced their 3rd presumptive positive HPAI H5 case of this fall (see below) - this time affecting a 4th Hawaiian  island (Kauaʻi).  

What was once unheard of has now become increasingly common now that the HPAI H5 virus has better adapted to seabirds (see 2022's Unprecedented `Order Shift' In Wild Bird H5N1 Positives), with many species; including gannets, gulls, guillemots and great skua now hosting the virus.

The behavioral shift has not gone unnoticed by Oceania (Australia/NZ) which have been on HPAI watch for several years (see Australia: Confirmation of H5 Bird Flu on Sub-Antarctic Heard Island).

First the announcement from the Hawaiian Department of Land and Natural Resources, after which I'll return with a bit more.

12/11/25 – STATE AGENCIES RESPOND TO THIRD POSSIBLE CASE OF HIGHLY PATHOGENIC AVIAN INFLUENZA IN HAWAIʻI

Posted on Dec 11, 2025 in Forestry & Wildlife, Main, News Releases, slider

HONOLULU – Three state agencies remain on alert after a third presumptive case of avian influenza was found in a wild bird — this time in an endangered native duck on Kauaʻi. Preliminary testing performed by the Hawaiʻi State Laboratory showed the bird was infected with an influenza A virus, though confirmation and subtype identification (e.g., H5N1) are pending further analysis by the National Veterinary Services Laboratories (NVSL).

A Koloa Maoli (Hawaiian duck) was found sick on November 26 at the U.S. Fish and Wildlife Service’s Hanalei National Wildlife Refuge in Hanalei, Kauaʻi. The bird died within 24 hours.

H5N1 is a highly infectious and often deadly subtype of influenza A that mainly affects birds. Human infections are rare but can occur with close contact. Hawaiʻi’s first detection of H5N1 occurred in November 2024 in a backyard flock on Oʻahu, followed by a hybrid duck found on Oʻahu’s North Shore. This year, two additional cases have been confirmed in migratory Koloa Māpu ducks—one on Oʻahu and one on Maui. This Kauaʻi detection is the first potential case in a native bird, likely introduced through infected migratory waterfowl.

The Hawaiʻi Department of Health (DOH), Department of Agriculture & Biosecurity (DAB), and Department of Land and Natural Resources (DLNR) continue coordinated monitoring of public health reports, poultry operations and wild bird populations for any signs of virus spread.

With migratory bird season underway, more birds traveling through the islands may carry avian diseases and it is recommended that the public avoid touching or handling wild birds, especially waterfowl or shorebirds.

If you encounter sick or dead birds, such as waterfowl:

• Avoid touching or handling wild birds, especially waterfowl or shorebirds.
• If capturing a dead or sick bird is necessary, wear gloves, minimize contact and follow biosafety protocols.
• To report multiple or unusual illnesses in poultry, livestock or other wild birds or animals, contact DAB’s Animal Industry Division at 808-483-7100, Monday through Friday from 7:45 a.m. to 4:30 p.m., or 808-837-8092 during non-business hours and holidays. Send email to DABIC@hawaii.gov

About H5N1/Avian Influenza:

• H5N1 is an avian influenza virus that mainly affects birds; human infections are uncommon but can happen following close contact with infected birds.
• The public risk in Hawaiʻi is currently low, so the DOH does not recommend restricting outdoor activities.
• Routine influenza vaccines in humans do not protect against H5N1; the best prevention is avoiding contact with sick or dead birds.

For more information, visit:

DOH: https://health.hawaii.gov/docd/disease_listing/avian-influenza/

DAB: https://dab.hawaii.gov/ai/ldc/avian-influenza-information/

This fall we've seen unprecedented numbers of avian flu reports across North America and much of Europe -  particularly in wild birds - but also affecting commercial and backyard flocks.

Credit ECDC/EFSA Avian influenza overview Sep–Nov 2025

After two less impactful years (see chart above), avian flu has reinvented itself and is back with a vengeance.  While it could fizzle again, right now there appears to be an immense amount of the virus circulating in wild birds, increasings the risks of spillovers into poultry, mammalian wildlife, and even humans.

Last July we looked at the results of a survey of stakeholders (backyard poultry owners, animal rescue, etc.) on their knowledge of HPAI (see Hawaii: Findings From DOH Bird Flu Survey For Backyard Flock Bird Owners And Bird Rescuers), which found sizeable knowledge gaps.

 

Two months ago, in UF/IFAS Extension: What Backyard Flock Owners Need to Know about Bird Flu (Influenza H5N1) we looked at some common-sense steps people who raise birds can take to reduce the risk of infection.

Admittedly, trying to predict what HPAI does next is a mug's game, but if there was ever a time to be extra diligent in avoiding exposure to wild birds, and for flock owners to increase their biosecurity, it is probably now. 

For some official advice from the ECDC/EFSA, you may wish to revisit:

Avian influenza in Europe: enhanced surveillance and strict biosecurity needed as detections surge

Eurosurveillance: Extended influenza seasons in Australia and New Zealand in 2025 due to the emergence of influenza A(H3N2) subclade K viruses

 

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Yesterday morning, in WHO DON: Seasonal influenza - Global situation, we took a side excursion to look at the most recent Australian Respiratory Surveillance Report (Dec 1st, 2025), which described their unusually prolonged flu 2025 flu season:

Nationally, the number of influenza cases has been consistently increasing since late October, which is unusual for this time of year. Current case numbers remain considerably higher than observed at the same time period in previous seasons (Figure 6).

– Several factors may be contributing to this out-of-season increase but the main driver is most likely influenza A(H3N2), in particular clade 2a.3a.1, subclade K

A few hours later, the ECDC Journal Eurosurveillance published the following Rapid communication on this exact subject. 

Important, because if the Australian experience is any guide, we could be in for a prolonged flu season in the Northern Hemisphere as well.

I've posted the link, and some excerpts, but you'll want to follow the link to read it in its entirety.

Extended influenza seasons in Australia and New Zealand in 2025 due to the emergence of influenza A(H3N2) subclade K viruses 
Clyde Dapat1,* , Heidi Peck1,* , Lauren Jelley2 , Tanya Diefenbach-Elstob1 , Tegan Slater2 , Saira Hussain1 , Phillip Britton3,4 , Allen C. Cheng5 , Tim Wood2 , Annaleise Howard-Jones3,4 , Yi Mo Deng1 , Jessica E. Miller1 , Q. Sue Huang2 , Ian G. Barr1,6

In 2025, influenza seasons in Australia and New Zealand were each prolonged due to the emergence of an influenza A(H3N2) variant of subclade K (formerly J.2.4.1). We describe the influenza epidemics overall in each country, with the phylogenetic characterisation of circulating viruses, and assess the dissemination of subclade K viruses, which thereafter were identified in most parts of the world. Antigenic characterisation of subclade K viruses found these to be distinct from prior circulating subclade J viruses and from the A(H3N2) strain A/Croatia/10136RV/2023 (H3N2)-like virus, which was included in the 2025 southern hemisphere (SH) and 2025/26 northern hemisphere (NH) vaccines.

Seasonal 2025 influenza epidemics in Australia and New Zealand
 
Influenza seasons vary somewhat each year in their onset, intensity, severity and duration. Many factors contribute to this variability such as temperature, rainfall, humidity, circulating virus types/subtypes, population immunity (vaccination or natural infections), as well as domestic and international travel [1-3]. The 2025 Australian influenza season had record numbers of laboratory-confirmed influenza cases since influenza became a notifiable disease in 2001 (457,906 cases from 1 January to 28 November 2025) [4] and an unusually long season stretching from May to November (Figure 1A). New Zealand had a more moderate season but with a longer than usual tail (Figure 1B) [5].

       (SNIP)

Discussion

The rapid rise of A(H3N2) influenza cases at the end of long influenza seasons in both Australia and New Zealand, provides evidence that the new subclade K virus variant is virologically fit and antigenically distinct from previously circulating H3N2 viruses. Based on the antigenic changes in the HA of the K viruses, the 2025/26 H3N2 NH vaccine component (i.e. A/Croatia/10136RV/2023-like virus) may have reduced effectiveness if K viruses circulate widely, and could result in increased cases and hospitalisations compared with recent years when A(H1N1)pdm09 predominated in many regions across Europe, Asia and North America [7].

This is the first time that such a variant has emerged so rapidly and spread so widely towards the end of the season in Australia−New Zealand and has continued to circulate into summer in Australia. This is unusual for A(H3N2) viruses but has been seen previously on occasions in Australia with influenza B viruses [11]. Late emerging A(H3N2) viruses also occurred in 2019 that resulted in a delay in the recommendation for the 2019/20 NH influenza vaccine A(H3N2) component, with an A/Kansas/14/2017-like virus finally being selected [12], and earlier in 2003 when A/Fujian/411/2002-like viruses emerged late in the 2002/03 season [13].

Importantly the Australian−New Zealand H3N2 K viruses were still susceptible to all licensed influenza antiviral drugs from testing performed at the WHO Centre (71/71 viruses tested with oseltamvir, zanamivir, laninamivir, peramivir and 240/240 virus sequenced for baloxavir marboxil mutations; full data not shown). Hence, these antivirals may be used to ameliorate the outcomes from subclade K virus infections. These drugs are most effective if administered within 48 hours of when symptoms first appear [14] and may have an increased role in treating severe infections. Encouragingly, despite high apparent transmissibility, there is no evidence to date of a clinical severity signal with K viruses. Additionally, a preliminary UK study found the typical range of vaccine effectiveness (VE) in line with age groups (2−12 years, 18−64 years and ≥ 65 years) against emergency department attendance or hospitalisation, during the early part of the season (29 September−2 November 2025) when K viruses were 87% prevalent [15]. If these VEs are borne out, then influenza vaccination will still be useful in reducing the impact of the disease.

This analysis has limitations. Most influenza A samples in both Australia and New Zealand are not subtyped and only a small proportion of influenza A(H3N2) viruses have had isolates generated and tested in HI assays and similarly only a fraction of viruses was sequenced and analysed phylogenetically. Additionally, only international HA and NA influenza sequences that were available on GISAID at the time of analysis were included in this study.

Conclusion 

Given the speed and size of the outbreaks of K viruses in Australia−New Zealand and the near global spread of these viruses already, it is likely that they will further expand during the NH winter season and persist for the remainder of 2025 and into 2026.

Careful clinical and epidemiological monitoring combined with timely virus sequencing and further VE studies, will determine the extent and impact that this new influenza A(H3N2) variant will have over the coming months, but countries should be prepared for increased demands on their healthcare systems if this variant predominates, as one might expect it will, based on current global trends.

       (Continue . . . )

Preprint: Vaccine-induced Antigenic Drift of a Human-origin H3N2 Influenza A Virus in Swine Alters Glycan Binding and Sialic Acid Avidity

 

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While desperate farmers, beleaguered politicians, and shell-shocked consumers are all looking for ways to reduce the burden of avian flu - and livestock vaccination seems the obvious solution - we must always be cognizant of the law of unintended consequences,

Over the years we've seen growing evidence that the use of non-neutralizing, poorly matched, or improperly applied, veterinary vaccines actually risks making matters worse (see PLoS Bio: Imperfect Poultry Vaccines, Unintended Results).

In 2014's EID Journal dispatch Subclinical Highly Pathogenic Avian Influenza Virus Infection among Vaccinated Chickens, China, the authors wrote:

HPAI mass vaccination played a crucial role in HPAI control in China. However, this study demonstrated multiple disadvantages of HPAI mass vaccination, which had been suspected (13,14). For example, this study showed that H5N1 subtype HPAI virus has evolved into multiple H5N2 genotypes, which are all likely vaccine-escape variants, suggesting that this virus can easily evolve into vaccine-escape variants.

This observation suggests that HPAI mass vaccination, which is highly effective in the beginning of an outbreak, may lose its effectiveness with time unless the vaccine strains are updated. Moreover, this study showed that vaccinated chicken flocks can be infected with vaccine-escape variants without signs of illness.

More recently, in 2021's J. Virus Erad.: Ineffective Control Of LPAI H9N2 By Inactivated Poultry Vaccines - China, the authors warned that China's current inactivated vaccines were no match against this rapidly evolving pathogen.

Last April, in NPJ Vaccines: Impact of Inactivated Vaccine on Transmission and Evolution of H9N2 Avian Influenza Virus in Chickens, we saw evidence that not only had inactivated vaccines failed to prevent - or even reduce - H9N2 in China's poultry, they may have driven viral evolution (including mammalian adaptations).

And just a little over a month ago (see MOA Announces New Guidelines to Expedite Animal Vaccine Strain Approvals) China tacitly admitted that many of their current animal vaccines (including against H9N2) are inadequate and/or suboptimal - and ordered major regulatory changes in order to accelerate updates. 

These vaccine problems extend far beyond China.

• In 2012's Egypt: A Paltry Poultry Vaccine, researchers examined the effectiveness of six commercially available H5 poultry vaccines used in Egypt and found only one actually appeared to offer protection.

• Six years later, another study (see Sci. Reports: Efficacy Of AI Vaccines Against The H5N8 Virus in Egypt) found `. . . most of the commercial poultry H5 vaccines used in the present study were ineffective. . . '

• in 2023's WUR: 2 of 4 H5 Poultry Vaccines Tested Appear Effective Against H5N1, researchers in the Netherlands found ineffective vaccines were still being marketed.

While these problems are no-doubt solvable, that will only come about if we acknowledge the risks, and commit to addressing them.  

All of which brings us to a new preprint on U.S. Government research which looks at the impact of swine-influenza vaccines in pigs, and how they too can help drive viral evolution.   

Although this study is on a different influenza A subtype (H3N2), affecting a different species (swine), it finds a similar pattern of vaccine-induced evolution.  Due to it length, and technical nature, I've just posted some excerpts. 

Follow the link to read it in its entirety.  I'll have a bit more after the break. 

Vaccine-induced antigenic drift of a human-origin H3N2 Influenza A virus in swine alters glycan binding and sialic acid avidity
Matias Cardenas, Pradeep Chopra, Brianna Cowan, C. Joaquin Caceres, Tavis K. Anderson, Amy L. Baker, Daniel R. Perez, Geert-Jan Boons, Daniela S Rajao
doi: https://doi.org/10.64898/2025.12.10.693614
This article is a preprint and has not been certified by peer review [what does this mean?].

Preview PDF

Abstract

Interspecies transmission of human influenza A viruses (FLUAV) to swine occurs frequently, yet the molecular factors driving adaptation remain poorly understood. Here we investigated how vaccine-induced immunity shapes the evolution of a human-origin H3N2 virus in pigs using an in vivo sustained transmission model.

Pigs (seeders) were vaccinated with a commercial inactivated swine accine and then infected with an antigenically distinct FLUAV containing human-origin HA/NA. Contact pigs were introduced two days later. After 3 days, seeder pigs were removed, and new contacts introduced. This was repeated for a total of 4 contacts.

Sequencing of nasal swab samples showed the emergence of mutations clustered near the HA receptor binding site, enabling immune escape and abolishing binding to N-glycolylneuraminic acid. Mutant viruses recognized α2,6-sialosides with 3 N-acetyllactosamine repeats, which are rare in swine lungs, while the parental virus bound structures with a minimum of 2 repeats. Adaptative HA mutations enhanced avidity for α2,6-linked sialic acid, likely compensating for the low abundance of extended glycans. Notably, residues outside the canonical HA binding pocket contribute to glycan binding, suggesting a trade-off between receptor breadth and avidity. These findings show that non-neutralizing immunity promotes viral adaptation by fine-tuning receptor engagement and immune evasion.

       (SNIP)

SIGNIFICANCE

Understanding how vaccination shapes influenza A virus (FLUAV) evolution across species barriers is critical for predicting and preventing zoonotic and reverse  zoonotic events.

Our study demonstrates that vaccine-induced immune pressure can drive antigenic drift in a human-origin H3N2 virus, altering HA receptor binding properties that could inadvertently facilitate adaptation to swine. These changes shifted glycan specificity toward extended poly-LacNAc structures and enhanced α2,6-linked  sialoglycans binding while abolishing Neu5Gc recognition. By revealing how non neutralizing immunity fine-tunes HA–glycan interactions by engaging antigenically relevant residues in glycan binding, this work highlights vaccination as an underappreciated driver of host adaptation and viral evolution. 

       (SNIP)

Overall, our findings demonstrate that vaccine-induced immunity in pigs can shape the evolution of human-origin H3N2 viruses. This process seems to select mutants with restricted receptor binding but enhanced a2,6-SA avidity while maintaining an optimal HA/NA balance. The fixation of F193Y highlights how immune escape and host adaptation can converge to promote viral fitness in a new host.

These results indicate that vaccination may inadvertently accelerate viral adaptation following a spillover by favoring mutation of antigenically relevant residues that can alter glycan selectivity and enhance binding to host-specific structures.

        (Continue . . . )

Properly done, poultry and/or livestock vaccination against novel flu should be both a safe and effective strategy, but we are going to need better (and continually updated) vaccines, along with finding ways to ensure they are being properly and consistently applied. 

Even then, we can't just `vaccinate and forget'. 

We will also need enhanced ongoing surveillance and testing of vaccinated flocks (looking for asymptomatic breakthrough infections), and the judicious use of quarantines and/or culling for breakthrough infections. 

None of which will be easy or cheap. 

But the evidence suggests, doing anything less risks creating even greater viral challenges down the road.  

TPWD Wildlife Health Alert: HPAI Detected in Multiple Areas Throughout Texas

 

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Although the USDA has confirmed 674 mammalian wildlife infections with HPAI across the country, this is undoubtedly a massive undercount, as many states simply do not aggressively look for, or report, cases. 

Texas has reported 28 detections since 2023 - mostly in skunks and domestic cats - with the most recent collection date in March of 2025.   

Texas has reported more recent detections of HPAI H5 in wild birds (n=11 in November 2025), however.

While they don't list specific recent examples, this week the Texas Parks and Wildlife Department (TPTD) has released a wildlife health alert, indicating that HPAI has been detected in multiple locations throughout the states. 

First the press release, after which I'll have a postscript. 

Wildlife Health Alert: Highly Pathogenic Avian Influenza Detected in Multiple Areas Throughout Texas

Dec. 9, 2025

Media Contact: TPWD News, Business Hours, 512-389-8030

AUSTIN —Texas Parks and Wildlife Department (TPWD) urges caution as highly pathogenic avian influenza (HPAI) is circulating among wild birds across the state as waterbirds and waterfowl migrate and congregate on their wintering grounds.

Detected in all 50 states across the U.S. and Puerto Rico, HPAI is a highly contagious zoonotic virus that transmits easily among wild and domestic birds. It can spread directly between animals and indirectly through environmental contamination.

What is Avian Influenza:

Avian Influenza, caused by influenza type A viruses, is a contagious viral disease that poses a major threat to the poultry industry and animal health. Migratory waterfowl and other waterbirds are a natural reservoir for this disease.

There are many strains of the virus that vary in severity based on the species affected. These strains are put into two general classifications— low pathogenic (LPAI) and highly pathogenic (HPAI). LPAI generally causes only minor illnesses and occurs naturally in migratory waterfowl. HPAI spreads rapidly and has a high death rate in birds.

Additionally, select mammal species are highly susceptible to HPAI including domestic cats, skunks, foxes, raccoons, bobcats, mountain lions and black bears.

Due to the ease of transmission, TPWD recommends wildlife rehabilitators remain cautious when intaking wild animals with clinical signs consistent with HPAI and quarantining animals to limit the potential for HPAI exposure to other animals within the facility. Backyard poultry may infect or be infected by contact with wild birds. If a wildlife rehabilitator suspects HPAI in an animal, contact TPWD within 24 hours of intake.

Clinical Signs and Transmission:

Clinical signs include neurological disease such as incoordination or stumbling, lethargy, trembling, seizures, lack of fear of people, coughing and sneezing and sudden death, though birds infected with HPAI may not always have outward signs of infection. The virus may spread in a variety of ways, including through contact with infected wild and domestic birds as well as by contaminated equipment, clothing and shoes of caretakers.

For mammals, transmission occurs primarily through the consumption of infected animal carcasses and contaminated equipment.

Currently, the transmission risk of avian influenza from infected birds to people remains low, but the public should take basic protective measures if contact with wild animals cannot be avoided. Public and health care professionals can find more information about HPAI in humans from the Texas Department of State Health Services. If you have contact with an HPAI-positive animal and develop signs of illness, immediately contact your health care provider and let them know about the exposure.

Prevention:

The public can assist in interrupting HPAI transmission by limiting all unnecessary contact with wild birds. Bird feeders and water sources should be cleaned at least every two weeks with a solution of one part household bleach to nine parts water. Change water in birdbaths every few days and regularly remove wet feed and seed from feed and water sources. Discourage the congregation of waterfowl around food, water sources and backyard flocks.

Game bird hunters should consider precautions such as:

• Disposing of carcasses properly
• Wearing gloves when processing
• Avoiding consumption or processing of any sick bird
• Cleaning and disinfecting tools between carcasses
• Cooking meat to proper temperatures

If you encounter a wild animal with signs consistent with HPAI, contact your local TPWD wildlife biologist.

Additional Resources:United States Department of Agriculture- Avian Influenza
https://www.aphis.usda.gov/livestock-poultry-disease/avian/avian-influenza
Texas Animal Health Commission- Highly Pathogenic Avian Influenza
https://www.tahc.texas.gov/emergency/avianinfluenza.html
Center for Disease Control (CDC)
https://www.cdc.gov/bird-flu/
Hunters- Protect your Poultry and Pet Birds
https://www.aphis.usda.gov/sites/default/files/fsc_hpai_hunters.pdf
Manage Wildlife to Prevent Avian Influenza
https://www.aphis.usda.gov/sites/default/files/fs-manage-wildlife-prevent-ai.508.pdf
Avian influenza- American Veterinary Medical Association
https://www.avma.org/resources-tools/animal-health-and-welfare/animal-health/avian-influenza

While this is a Texas-specific health alert, it is a pretty safe bet that similar risks exist in every state in the nation, and in most countries around the world. 

This week Ohio made national headlines after 70 vultures were found dead on a school campus in Pierce Township, while in Manitoba, Canada scores of dead wild geese have reportedly died from HPAI H5N1. 

What was once a rare, or newsworthy, event in North America has now increasingly commonplace.

Hopefully hunters, pet owners, and those who raise backyard birds are taking note and following the guidance, as the last thing we need to do is to inadvertently give these viruses a helping hand. 

WHO DON: Seasonal influenza - Global situation

 

Credit WHO Global Respiratory Rept #556 

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For the past 5 weeks we've been following reports of unusual seasonal flu activity - both in the Southern and Northern Hemispheres - which has been attributed to the recent emergence of a `drifted' H3N2 virus (subclade K) over the past few months in the Southern Hemisphere. 

While the WHO has already selected two new strains (H1N1 and H3N2) for next year's Southern Hemisphere flu vaccine, we are going into winter with a vaccine that was formulated before this new variant emerged. 

Since decisions must be made more than 6 months in advance on what flu strains to include, there is always the chance of mutations emerging, particularly in the H3N2 subtype - which typically evolves at faster rate than H1N1 (see The Enigmatic, Problematic H3N2 Influenza Virus).

While there are reasons to believe the existing vaccine will be at least `partially protective' - at least against severe infection (see UKHSA Preprint: Early Influenza Virus Characterisation and Vaccine Effectiveness in England in Autumn 2025, A Period Dominated by Influenza A(H3N2) Subclade K) - we won't have useful VE (vaccine effectiveness) numbers until January. 

Over the past month we've seen reports of unusually early, and robust, flu outbreaks in places like Japan, South Korea, China, and much of Europe. Some  countries are now urging the public to wear face masks in public, and many school closures have been reported. 

Somewhat remarkably, Australia's flu season - which would normally have ended in August - continues (albeit well off the highs of July) during their summer (see Australian CDC chart below)

The Australian Respiratory Surveillance Report (Dec 1st, 2025) describes this unusual extended flu season, and attributes it to the emergence of the drifted H3N2 virus. 

Nationally, the number of influenza cases has been consistently increasing since late October, which is unusual for this time of year. Current case numbers remain considerably higher than observed at the same time period in previous seasons (Figure 6).

– Several factors may be contributing to this out-of-season increase but the main driver is most likely influenza A(H3N2), in particular clade 2a.3a.1, subclade K

– Subclade K has developed seven new mutations, making it different enough from the 2025 southern hemisphere influenza vaccine reference strain (subclade J.2). As a result, the influenza A(H3N2) subclade K strain now circulating is less responsive to antibodies produced by this year’s vaccine compared to the influenza A(H3N2) strain circulating earlier in the season.

– Despite this, the influenza vaccine still provides important protection against severe illness and complications from influenza. The current influenza A(H3N2) subclade K viruses also show reasonable match to the 2026 proposed southern hemisphere vaccine strain.

– This situation reflects what has recently been reported in northern hemisphere countries,where the influenza season has started unusually early.

Overnight the WHO published a lengthy DON (Disease Outbreak News) report on this `drifted' H3N2 virus, and the impacts it is having around the globe. 

As we've noted often, surveillance and reporting isn't always as timely or robust as we'd like (see From Here to Impunity), and so the WHO is operating on limited data. 

Due to its length, I've only posted some excerpts. Follow the link to read it in its entirety.  I'll have a bit more when you return.

Seasonal influenza - Global situation
10 December 2025

Situation at a glance

Seasonal influenza (‘the flu’) is an acute respiratory infection caused by influenza viruses that circulate globally and year-round. It can cause illness ranging from mild to severe, sometimes resulting in hospitalization or death. Seasonal influenza activity has increased globally in recent months, with an increased proportion of seasonal influenza A(H3N2) viruses being detected. This rise coincides with the onset of winter in the northern hemisphere and an increase in acute respiratory infections caused by influenza and other respiratory viruses typically observed at this time of year.

Although global activity remains within expected seasonal ranges, early increases and higher activity than typical at this time of year have been observed in some regions. Seasonal influenza viruses, including A(H3N2) viruses, continually evolve over time.

Since August 2025, there has been a rapid increase of A(H3N2) J.2.4.1 alias K subclade viruses detected from several countries based on available genetic sequence data. These subclade K viruses have several changes from related A(H3N2) viruses. Current epidemiological data do not indicate an increase in disease severity, although this subclade marks a notable evolution in influenza A(H3N2) viruses. Early estimates suggest that the influenza vaccine continues to provide protection against hospital attendance in both children and adults, even though its effectiveness against clinical disease during the current season remains uncertain. 

Vaccines remain essential, especially for people at high risk of influenza complications and their caregivers. Even if there are some genetic differences between the circulating influenza viruses and the strains included in the vaccines, the seasonal influenza vaccine may still provide protection against drifted viruses and the other virus strains included in the vaccine. Vaccination is still expected to protect against severe illness and remains one of the most effective public health measures. WHO continues to monitor global influenza activity and influenza viruses, supports countries in surveillance capacity and updates guidance as needed.

(SNIP)

Genetic characteristics of recent seasonal influenza viruses

Influenza A(H1N1)pdm09 and influenza B/Victoria lineage viruses continue to circulate in all regions albeit at low levels.

Influenza A(H3N2) viruses

Based on genetic sequence data available in GISAID, a mixture of A(H3N2) haemagglutinin (HA) clades and subclades are currently circulating globally; however, there has been a recent and rapid rise in a particular subclade of A(H3N2), J.2.4.1 (alias subclade K Nextclade/Nextstrain nomenclature). A(H3N2) subclade K viruses have genetically drifted from related J.2.4 viruses and have several amino acid changes in their HA in comparison. Detections of subclade K viruses are increasing in many parts of the world, with the exception, to date, of South America. Subclade K viruses were particularly evident from August 2025 in Australia and New Zealand and have now been detected in more than 34 countries over the last 6 months.

WHO risk assessment

Seasonal influenza activity has increased globally in recent months, and influenza A(H3N2) viruses are predominant. This rise coincides with the onset of winter in the northern hemisphere. Epidemics and outbreaks of seasonal influenza and other circulating respiratory viruses can place significant pressure on healthcare systems. Although global activity remains within expected seasonal ranges, early increases and higher activity than typical at this time of year have been observed in some regions.

Seasonal influenza could place significant pressure on healthcare systems even in non-temperate countries. Genetically drifted influenza A(H3N2) viruses, known as subclade K viruses, have been detected in many countries. While data on how well the vaccine works against clinical disease this season are still limited, vaccination is still expected to protect against severe illness and remains one of the most effective public health measures.

        (Continue  . . . )

While likely hampered by reduced reporting over the Thanksgiving Holidays, last week the CDC's FluView reported that the vast majority of H3N2 viruses characterised in the United States since the end of September are now subclade K. 

During Week 48, of the 348 influenza viruses reported by public health laboratories, 341 were influenza A and 7 were influenza B. Of the 280 influenza A viruses subtyped during Week 48, 44 (15.7%) were influenza A(H1N1)pdm09, and 236 (84.3%) were A(H3N2).

• A new influenza A(H3N2) virus subclade J.2.4.1, also recently renamed "H3N2 subclade K," was identified by CDC in August 2025. These viruses have small changes in their hemagglutinin gene and have been antigenically characterized as "antigenically drifted" in comparison to the virus selected as the A(H3N2) component of the U.S. 2025-26 seasonal influenza vaccines.

• Among 91 influenza A(H3N2) viruses collected since September 28, 2025, that underwent additional genetic characterization at CDC, 86.8% belonged to subclade K.

Give the historic severity of H3N2 - particularly in the elderly - and the rapid spread (and unusual persistence in Australia) of this emerging subclade, I'm glad I got this year's flu vaccine, even if its effectiveness ends up being diminished. 

I am admittedly augmenting its protection by wearing a KN95 in public, and using copious amounts of hand sanitizer.  

While influenza is always unpredictable, the early signs suggest we could be in for another severe season, so anything you can do to avoid infection should be a high priority.