The Lancet: The Threat of Another Coronavirus Pandemic

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Although influenza A has historically been the cause of most major respiratory pandemics, three times between 2002 and 2020 we watched as (3 different) novel  coronaviruses emerged from the wild, and threatened  a global health crisis. 

• First, in 2002, SARS-CoV (see SARS & Remembrance) spread hidden in China for months before it burst on the international scene.  Luckily, its inability to spread asymptomatically - and strict quarantines - limited its impact. 

• Ten years later (2012) another coronavirus - MERS-CoV - began spilling over from camels on the Arabian Peninsula, and then spreading (primarily in hospitals) from human-to-human (see Ziad Memish: Two MERS-CoV Hospital Super Spreading Studies).

• While deadlier than SARS-CoV, MERS-CoV never quite achieved the same level of transmission, and so outbreaks have remained limited. Still, thousands have been confirmed infected, and roughly 35% have proven fatal. 

• And of course in 2020, a novel coronavirus (SARS-CoV-2) sparked the worst human pandemic in over 100 years.  While estimates vary, many experts put the number of deaths in the tens of millions. 

MER-CoV and SARS-CoV are still very much with us - both continue to cause illness and death - and most importantly, both continue to evolve (see Nature: CoV Recombination Potential & The Need For the Development of Pan-CoV Vaccines).

All of which suggests a new, more virulent COVID variant, or a more transmissible MERS-CoV mutation, could still be in our future (see Health Sci Rpts: Pathogenicity and Potential Role of MERS-CoV in the Emergence of “Disease X”).

But at the same time we've seen numerous reports of newly discovered coronaviruses circulating in the wild which also appear to have zoonotic potential. Just a few, of many, include:

Preprint: A Divergent Betacoronavirus with a Functional Furin Cleavage Site in South American Bats

J. of Infection: Novel Coronaviruses Identified in Livestock

Viruses: Novel Rodent Coronavirus-like Virus Detected Among Beef Cattle with Respiratory Disease in Mexico

Nature: Study on Sentinel Hosts for Surveillance of Future COVID-19-like Outbreaks

Preprint: Human Cell adaptation of the Swine Acute Diarrhea Syndrome Coronavirus Spike Protein

While it may seem overly sanguine to ask how we are preparing to deal with another coronavirus pandemic when we seem incapable of dealing with far more immediate threats that are already on our plate (i.e. COVID & HPAI) - given the above examples - is still a question worth asking. 

Today we've a short, but somewhat technical commentary on recently identified ACE2-using merbecoviruses - like HKU5-CoV-2 - which may represent potential future coronavirus pandemic threats. 

Interestingly, this article suggests that prior COVID-19 infection is unlikely provide meaningful antibody protection against these HKU5-like merbecoviruses, reporting that sera from people who had SARS‑CoV‑2 did not neutralize HKU5 in vitro. 

While the serum from patients with a previous SARS-CoV-2 infection contained antibodies that failed to neutralise HKU5-CoV, three of 28 patients with a past MERS-CoV infection harboured antibodies that neutralised HKU5-CoV.7  This finding highlights the vast antigenic differences between merbecoviruses and sarbecoviruses, which likely stem from structural changes in the spike protein.

Due to its technically dense content, I've elected to post the link and a very brief excerpt. Follow the link to read it in its entirety.  I'll have a bit more after the break.

The threat of another coronavirus pandemic: how are we preparing for it?

Marcus G Maha,c ∙ Neha Dikshita,c ∙ Ramona Alikiiteaga Gutierreza,b ∙ David Chien Lyea,b,c,d,e,f ∙ Lin-Fa Wanga,c,g linfa.wang@duke-nus.edu.sg

Published December 12, 2025

DOI: 10.1016/j.lanmic.2025.101308 External Link

Copyright: © 2025 The Author(s). Published by Elsevier Ltd.

User License: Creative Commons Attribution (CC BY 4.0)

 

Merbecovirus is a subgenus within the genus Betacoronavirus that is genetically distinct from Sarbecovirus (eg, SARS-CoV-2). Recently, a few merbecoviruses isolated from the bat genus Pipistrellus were characterised and shown to have the ability to bind to angiotensin-converting enzyme 2 (ACE2) as an entry receptor.

These merbecoviruses include HKU5-CoV isolated from Hong Kong,1 HKU5-CoV-2 isolated from China,2 PnNL2018b isolated from the Netherlands,3 and MOW15-22 isolated from Russia.3 

This unexpected ability to bind to ACE2 was first observed in the African bat merbecoviruses NeoCoV and PDF-2180.4 Furthermore, these bat merbecoviruses bind only to ACE2, whereas the prototype merbecovirus MERS-CoV binds only to dipeptidyl peptidase-4 (DPP4).

(SNIP)

Coronaviruses will continue to remain a threat to public health. In this view, the scientific community can better prepare the world through the formation of the CORC-CoV, which fosters increased global cooperation, in line with the newly minted pandemic agreement. The comprehensive road map being developed by the CORC-CoV will also serve to engage funders towards supporting global efforts to overcome the identified primary research challenges and address key needs essential for advancements in the field of coronavirus research. Most importantly, the road map will help to drive priority research activities in preparation for the next coronavirus pandemic that could occur at any time.

(Continue . . . )

While we've heard a lot of voices urging stepped up surveillance, reporting, and pandemic preparedness in the wake of the last crisis (see WPRO Table-Top Exercise Crystal: A `Bovine' Novel Flu Outbreak Scenario), it is far less clear whether anyone in power is truly listening. 

Special interests, economic concerns, and the desire for short-term political gains all appear to cancel out - or marginalize - those voices. 

While I've no special insight into what will spark the next global health crisis - when that will come, or how severe it might be - history tells us another pandemic is inevitable. 

Assuming, of course, that we're actually listening. 

 

USDA: Wisconsin Becomes 18th State to Detect HPAI H5N1 in Dairy Cattle

 

#18,989

While the above graphic from the USDA's National Milk Testing Strategy (NMTS) website hasn't been updated to show it yet, late yesterday the USDA announced that Wisconsin - the second-largest milk producer in the U.S. - has at least one herd that has tested positive for HPAI H5N1.

First, the USDA's announcement, after which I'll have a bit more.

USDA Confirms Highly Pathogenic Avian Influenza in a Dairy Herd in Wisconsin

Contact: aphispress@usda.gov
Milk Supply Safe; Considered Low Risk to Human Health and Safety
WASHINGTON, DC- December 14, 2025 – Today, the U.S. Department of Agriculture’s Animal and Plant Health Inspection Service (APHIS) National Veterinary Services Laboratories (NVSL) confirmed via PCR (polymerase chain reaction) and ELISA (Enzyme-Linked Immunosorbent Assay) assay a detection of highly pathogenic avian influenza (HPAI) H5 clade 2.3.4.4b in a dairy cattle herd in Wisconsin. APHIS will complete genetic sequencing and announce final results as soon as they are available. This confirmation was a result of routine National Milk Testing Strategy testing, not pre-movement surveillance.

This marks the first known case of HPAI in cattle in Wisconsin. While dairy cattle in a total of 18 states have been infected since the start of the outbreak in March 2024, APHIS has seen cases in only a small number of states this year. APHIS is working closely with the Wisconsin Department of Agriculture, Trade, and Consumer Protection to conduct additional on-farm investigations, diagnostic testing, and epidemiological data collection to better understand the detection and prevent further disease spread.

The detection does not change USDA’s HPAI eradication strategy. Biosecurity is still key to mitigating the risk of disease introduction or spread between premises. APHIS recommends enhanced biosecurity measures for all dairy farms. Producers should immediately report any livestock with clinical signs, or any unusual sick or dead wildlife, to their state veterinarian. 

This detection does not pose a risk to consumer health or affect the safety of the commercial milk supply. The U.S. Food and Drug Administration is confident that pasteurization is effective at inactivating HPAI virus, and that the commercial, pasteurized milk supply is safe. Dairies are required to send only milk from healthy animals into processing for human consumption; milk from impacted animals is being diverted from the commercial milk tank or destroyed so that it does not enter the human food supply.

According to the U.S. Centers for Disease Control and Prevention (CDC), HPAI viruses circulating in birds and U.S. dairy cattle pose a low risk to the general public in the United States. However, people who have job-related or recreational exposures to infected birds or mammals are at higher risk of infection and should take appropriate precautions outlined in CDC guidance.

While reports of infected dairy herds have dwindled markedly during the second half of 2025, the USDA does not publish data on reinfected herds, as noted below by the California Department of Food & Agriculture website, and it isn't entirely clear what percentage of U.S. herds are currently tested on a regular basis.  

National Detections

This nationwide outbreak of H5N1 Bird Flu began in poultry in 2022 and was first detected in US dairy cattle in March 2024. All national detections in cattle can be found on the USDA website at: HPAI Confirmed Cases in Livestock | Animal and Plant Health Inspection Service (usda.gov). All national detections in poultry can be found on the USDA website at: Confirmations of Highly Pathogenic Avian Influenza in Commercial and Backyard Flocks | Animal and Plant Health Inspection Service (usda.gov)

Note: The USDA website reports new (first time detections) in dairies; it does not capture when a herd is cleared, ongoing cases, or reinfections on premises that had previous detections.

It will be of considerable interest to learn which genotype of HPAI H5N1 has been detected.  During all of 2024, only genotypes B3.13 was detected in cattle, but in early 2025 genotype D1.1 was reported in at least 2 states. 

For more information on the USDA's National Milk Testing Strategy you may wish to visit: 

Frequently Asked Questions: National Milk Testing Strategy

EID Journal Dispatch: Novel Highly Pathogenic Avian Influenza A(H5N1) Virus, Argentina, 2025

 

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Last August, in H5Nx: Reassort & Repeat, we looked at HPAI's promiscuous ways, and its propensity to reinvent itself - via reassortment - after it meets up with compatible LPAI viruses.  

Twenty years ago, H5N1's range was primarily limited to Southeast Asia, and so its reassortment opportunities were limited to LPAI viruses common to the region. 

But a chance reassortment near Qinghai Lake, Tibet in 2005 produced a more biological `fit', and far more easily carried (by migratory birds) clade 2.2 of the virus (see H5N1 Influenza Continues To Circulate and Change 2006 by Webster et. al.), which led to the first major diaspora of the virus (eventually spreading to Europe, the Middle East, and Africa). 

Over the years, as the virus spread around the globe, it encountered - and reassorted with - scores of  different LPAI viruses, producing hundreds of new clades, subclades, genotypes, and even new subtypes (H5N5, H5N6, H5N9, etc.).

While many were biological failures, some proved competitive enough to advance the spread, evolution, and diversity of the virus. We saw huge changes to HPAI in 2014 (changeover to H5N8), in 2016 (the first major European Epizootic), and in 2017 the virus crossed the Equator on its way to South Africa.

As H5's range increased, so did its genetic diversity, giving it even more reassortment opportunities. While it was growing stronger,  HPAI's first attempt to invade the Western Hemisphere (in 2014-2015) fizzled after 6 about months (see map below).

In 2020 the virus reassorted back to H5N1 - and having become even more `biologically fit' - in 2021 it make a far more successful 2nd invasion of the western hemisphere. 

Remarkably, within months of arriving in North America, it had already generated more than 100 new genotypes, and for the first time became capable of infecting mammalian livestock (goats, cattle, alpaca, etc.)

The pattern has been pretty consistent; as HPAI spreads, it encounters new opportunities to increase its genetic diversity. It is one of the reasons why its recent spread to Hawaii, and its feared spread into Oceania, are of great concern. 

Today we've a report from South America, published in the CDC EID Journal, which describes a unique 4:3:1 triple-reassortment of HPAI H5N1 detected in a mixed backyard flock (chickens, ducks, and turkeys) in Chaco Province, northern Argentina.

This outbreak was notable because the infected flock presented with severe, and atypical (dominated by diarrhea) symptoms. The authors wrote: 

The predominance of gastrointestinal signs suggests possible shifts in tissue tropism or virulence. Also, the detection of a North American NP segment not previously identified in LPAI viruses from Argentina or elsewhere in South America highlights the need to strengthen regional AIV surveillance, even in the absence of active HPAI circulation.

 I've posted the link, and some excerpts, from the dispatch below. Follow the link to read it in its entirety.  I'll have a brief postscript when you return.

Volume 31, Number 12—December 2025
Dispatch
Novel Highly Pathogenic Avian Influenza A(H5N1) Virus, Argentina, 2025

Ralph E.T. Vanstreels, Martha I. Nelson, María C. Artuso, Vanina D. Marchione, Luana E. Piccini, Estefania Benedetti, Alvin Crespo-Bellido, Agostina Pierdomenico, Thorsten Wolff, Marcela M. Uhart, and Agustina Rimondi

Abstract

Genomic sequencing of reemerging highly pathogenic avian influenza A(H5N1) virus detected in Argentina in February 2025 revealed novel triple-reassortant viruses containing gene segments from Eurasian H5N1 and low pathogenicity viruses from South and North American lineages. Our findings highlight continued evolution and diversification of clade 2.3.4.4b H5N1 in the Americas.

Highly pathogenic avian influenza (HPAI) viruses were introduced to South America in 2022 by migratory birds from North America. The viruses belonged to the 2.3.4.4b clade of HPAI A(H5N1) virus that became widespread in Europe in 2020 and spread to North America in 2021. The trajectory of H5N1 in South America has differed from H5N1 in North America in several critical ways. First, nearly all South America outbreaks stem from a single introduction of H5N1 viruses from North America (1,2), whereas the North America epizootic was reseeded by multiple independent introductions from Europe and Asia (A1–A6) (3,4). Second, South America H5N1 outbreaks were driven by a single genotype (B3.2) that was introduced from North America and remained genetically stable during its spread across South America. In contrast, H5N1 viruses in North America underwent frequent reassortment with low pathogenicity avian influenza (LPAI) viruses, prompting new genotype nomenclature (using B, C, D) (3). Third, South America’s H5N1 epizootic is unique in establishing mammal-to-mammal transmission in marine mammals, enabled by the H5N1 (B3.2) virus acquiring mammalian-adaptive polymerase basic (PB) 2 mutations (Q591K and D701N) (1,2). That pattern has not occurred in North America, where H5N1 spillover into terrestrial and marine mammals was transient, except in United States dairy cattle (3).

Beyond the ecologic devastation among coastal wildlife, in 2023, H5N1 (B3.2) virus spread widely in birds across mainland South America, leading to poultry and wild bird outbreaks (5–8). Although in 2024 HPAI outbreaks occurred in Brazil and Peru (World Organisation for Animal Health, https://wahis.woah.orgExternal Link), there were no detections in Argentina during March 2024–January 2025.

The Study

On February 11, 2025, Servicio Nacional de Sanidad y Calidad Agroalimentaria (SENASA; Buenos Aires, Argentina), Argentina’s national organization for agricultural health and safety, was notified of an outbreak in a mixed backyard flock (chickens, ducks, and turkeys) in Chaco Province, northern Argentina. The flock experienced high mortality (33/81 chickens, 37/99 ducks) in just 1 week. When we inspected the living flock, two thirds of the remaining 48 chickens had diarrhea and 1 of the remaining 62 ducks was lethargic; 2 turkeys were asymptomatic.

The household was located within a remnant fragment of the Dry Chaco biome, a hot and semi-arid tropical dry forest, surrounded by agriculture cropland. The affected flock had free access to a small pond frequently visited by wild waterfowl (Appendix 1). We depopulated and disinfected the area. We inspected backyard poultry within the 3 km perifocal zone (1 household) and the 3–10 km surveillance zone (7 households) and detected no illness or death. We did not find any affected wildlife on site.

       (SNIP) 

Conclusions

We have documented a reassortment event between HPAI H5N1 and endemic South America LPAI viruses. South American PB2 and PA segments are divergent from global AIV diversity (9) (Figure 1), indicating reassortment has expanded H5N1 polymerase diversity. Although the H5N1-Arg_Feb2025 viruses have exchanged 5 gene segments, they retained the original Eurasian MP segment (Figure 2), which remains conserved in most reassortant H5N1 viruses in North America. That segment conservation suggests the Eurasian MP segment might confer a selective advantage in HPAI H5 viruses. To date, we found no evidence of those novel 4:3:1 triple reassortant viruses in other South America countries; however, if future detections confirm wider spread, designation of a new H5N1 genotype would be warranted. Of consequence, genotyping tools such as the US Department of Agriculture’s GenoFlu should be expanded to include South American lineage genes for systematic classification of new virus genotypes.

(SNIP)

Further research on the diversity of LPAI viruses circulating in Neotropical wildlife will be essential to understand potential interactions between H5N1 and South American lineage strains and to assess the long-term consequences of the introduction of HPAI viruses into the region. Our findings underscore the critical importance of sustained influenza surveillance coupled with whole-genome sequencing to track the evolution of HPAI H5N1 and support efforts to control and mitigate its effect on domestic animals, wildlife, and human health.

Dr. Vanstreels is a veterinarian and an associate researcher with the Karen C. Drayer Wildlife Health Center at the University of California, Davis. His research interests include South American and Antarctic wildlife health, with a special interest in the ecology and effects of highly pathogenic avian influenza H5N1 on wild bird and marine mammal populations.

As the following FAO map illustrates, there are large swaths of the globe where the HPAI virus is presumably circulating, but which provide little (or no) surveillance and/or reporting.  

Blind spots include all of Russia, Central Asia, much of Africa, Northern Canada, and the interior of South America (note: Australia/NZ are testing, but the virus has not shown up yet).

While many of these  regions are impossibly remote, or lack the resources to do in-depth surveillance, there are many countries that simply choose not to report outbreaks for political or economic reasons.

Once again (see here, here, here, here, and here) the authors of today's report call for improved influenza surveillance and the timely reporting of data. 

And rightly so - because with rapidly evolving HPAI viruses - what we don't know can hurt us.  

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

#18,986

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.

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