WHO: Candidate Vaccine Viruses for Pandemic Preparedness - Feb 2026

Credit NIAID

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In addition to deciding which influenza viruses to include in the next seasonal flu vaccine (see WHO Recommendations for Influenza Vaccine Composition for the 2026-2027 Northern Hemisphere Influenza Season), twice each year flu researchers are asked by WHO to advise on the development of new CVVs (Candidate Vaccine Viruses) for zoonotic influenza.

While our attentions are primarily focused on the clade 2.3.4.4b H5N1 virus, there are literally dozens of other zoonotic influenza A viruses circulating around the world (see CDC IRAT list), all of which are believed to have some degree of pandemic potential.

Each year new variants - subclades, subtypes, or genotypes - emerge, and the WHO must decide if they warrant the creation of a CVV. Since H5 viruses evolve rapidly, many older CVVs no longer match circulating strains.

Having a proven CVV already tested and approved can save valuable time if  rapid production and distribution of a pandemic vaccine are ever required.

And over the past two decades, the WHO has recommended a lot of them (see list below). Forty-six are approved and available, and 6 are pending. And that's just for H5 subtypes.

They WHO has also approved 22 H7 CVVs (20 available, 2 pending), and 11 H9 CVVs (8 available, 3 pending), along with a smattering of other subtypes (H1, H3, H10, etc.).

This week the WHO published a 13-page update which contains background information on a wide range of novel avian and swine flu viruses detected over the past 6 months.  

While they cite ongoing antigenic changes - particularly among the H5Nx panoply of viruses - in the end only one new CVV was recommended for development; a new A/Hunan/40087/2025-like H9N2 CVV.

We've been following concerning antigenic changes in H9N2 viruses for quite some time (see China CDC Weekly: Epidemiological and Genetic Characterization of Three H9N2 Viruses Causing Human Infections — Changsha City, Hunan Province, China, April 2025).

While no new H5 CVVs were recommended, antigenic characterization is still pending on a number of recent human H5 infections, including last September's H5N2 case from Mexico, and several recent  H5N1 cases in Cambodia (clade 2.3.2.1e), along with a number of poultry isolates collected from Egypt, Laos, and Brazil. 

This report also finds that the recent H5N5 virus isolated from a human in Washington State showed reduced reactivity to existing CVVs.

The HA1 of the A(H5N5) virus from the human case in the United States of America had five amino acid substitutions relative to the A/Astrakhan/3212/2020 CVV, including a gain of a potential glycosylation site. Post-infection ferret antisera raised against clade 2.3.4.4b A/American Wigeon/South Carolina/22-000345-001/2021, A/Ezo red fox/Hokkaido/1/2022 and A/Astrakhan/3212/2020 CVVs showed reduced reactivity to the A(H5N5) virus.

For now, however, the WHO has decided the threshold has not been met to justify recommending the creation of an H5N5 CVV.  

I've only posted the summary, follow the link to read it in its entirety. I'll have a bit more after the break. 

Genetic and antigenic characteristics of zoonotic influenza A viruses and development of candidate vaccine viruses for pandemic preparedness

February 2026

The development of influenza candidate vaccine viruses (CVVs), coordinated by the World Health Organization(WHO), remains an essential component of the overall global strategy for influenza pandemic preparedness.

Selection and development of CVVs are the first steps towards timely vaccine production and do not imply a recommendation for initiating manufacture. National authorities may consider the use of one or more of these CVVs for pilot lot vaccine production, clinical trials and other pandemic preparedness purposes based on their assessment of public health risk and need.

Zoonotic influenza viruses continue to be identified and evolve both antigenically and genetically, leading to the need for additional CVVs for pandemic preparedness purposes. Changes in the antigenic and genetic characteristics of these viruses relative to existing CVVs and their potential risks to public health justify the need to develop new CVVs.

This document summarizes the antigenic and genetic characteristics of recent zoonotic influenza viruses and related viruses circulating in animals1 that are relevant to CVV updates. Institutions interested in receiving these CVVs should contact WHO at gisrs@who.int or the institutions listed in announcements published on the WHOwebsite2.

       (Continue . . . )

While having a closely-matched CVV might shave weeks or even months off the time it would take to develop, manufacture, and deploy a pandemic vaccine, there are still many obstacles to overcome.  

Any flu jab would likely require 2 shots - 30 days apart - and even under the best case scenarios, it would likely take 6 months or longer before substantial quantities of vaccine are available to the public. 

Some past blogs on some of the logistics of developing a pandemic vaccine include:

Referral: SCI AM - A Bird Flu Vaccine Might Come Too Late to Save Us from H5N1

NPJ Vaccines: Modeling the Impact of Early Vaccination in an Influenza Pandemic in the United States

How The WHO & CDC Are Developing Candidate H5N1 Vaccines

Manufacturing Pandemic Flu Vaccines: Easier Said Than Done

FluView Week 7: Influenza Remains Elevated & Additional Reports of Antiviral Resistance

 

https://www.cdc.gov/fluview/surveillance/2026-week-07.html

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Three months into this year's influenza season and flu activity remains elevated across much of the country (see map above), although we are seeing a decided shift from influenza A (primarily H3N2) to influenza B (see chart below).

While the big story of this year's flu season has been the emergence of a `drifted' H3N2 subclade K virus, another aspect we've been following have been sporadic reports around the world of reduced oseltamivir effectiveness against H1N1 due to NA-I223V and NA-S247N amino acid substitutions.

A few blogs include:

Eurosurveillance: Expansion of influenza A(H1N1)pdm09 NA:S247N Viruses with Reduced Susceptibility to Oseltamivir, Catalonia, Spain, and in Europe, July to October 2025

China: National Influenza Center Reporting Increased Oseltamivir Resistance in Seasonal H1N1

Taiwan CDC Statement On Increased Antiviral Resistance in Seasonal H1N1 Cases in 2025

Since 2009, global resistance to oseltamivir has run < 1%, although we've seen sporadic community clusters of H275Y mutations (see here, here, and here) and low‑levels of  I223V/S247N reported (see here and here). 

Over the entire 2024-2025 flu season - out of 1697 H1N1 viruses tested - only one carried the NA-I223V and NA-S247N amino acid substitutions.

Reassuringly, during the first 13 weeks of the 2025-2026 flu season (Oct - Dec) the CDC reported zero elevated resistance among the first 193 H1N1 viruses tested (see screenshot from FluView Wk 53).  

On January 10th (Fluview Wk 1), however, the CDC reported 2 (out of now 224) H1N1 viruses (0.2%) tested showed `reduced inhibition by oseltamivir' due to amino acid substitutions NA-I223V and NA-S247N. 

Two weeks ago, in FluView Week 5: Influenza Remains Elevated & Slight Uptick In Antiviral Resistance, we saw that count had increased to 7 reduced inhibition and 3 highly resistant (due to the more worrisome H275Y mutation).

Yesterday's FluView (week 7) - based now on 517 H1N1 isolates tested since October - reports 3 more reduced inhibition (n=10) and a 4th with highly reduced inhibition.

Four A(H1N1)pdm09 viruses had NA-H275Y amino acid substitution conferring highly reduced inhibition by oseltamivir and peramivir. Ten A(H1N1)pdm09 viruses had amino acid substitutions NA-I223V and NA-S247N and showed reduced inhibition by oseltamivir. Two B viruses had amino acid substitution NA- M464T and showed reduced inhibition by peramivir.

The impact of the H275Y mutation on oseltamivir resistance is far greater than I223V/S247N, but the stacking of H275Y with either I223V or S247N can greatly enhance the effect.

Although elevated above the historic baseline, these latest numbers still remain fairly low, and should not affect clinical decisions regarding antiviral treatment. 

But as a trend, they are very much worth noting.  

Which is why we'll be watching future reports to see if these numbers plateau, or continue to rise.  

WHO Recommendations for Influenza Vaccine Composition for the 2026-2027 Northern Hemisphere Influenza Season

Credit ACIP
 

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Twice each year international influenza experts meet to discuss recent developments in human and animal influenza viruses around the world, and to decide on the composition of the next influenza season’s flu vaccine.

Due to the time it takes to manufacture and distribute a vaccine, decisions on which strains to include must be made at least six months in advance. 

As occasionally happens, that can provide a window of opportunity for `drifted' or mutated flu strains to emerge, and spread globally (see last Nov's Increasing Concerns Over A `Drifted' H3N2 Virus This Flu Season).

Earlier this week, in Preprint: Near Real-time Data on the Human Neutralizing Antibody Landscape to Influenza Virus as of Early 2026 to Inform Vaccine-strain Selection, we looked at a `near real-time' assessment of the human neutralizing antibody landscape against currently circulating influenza A viruses.

A review which found that most people have low antibody defenses against recently emerged H3N2 subclade K and H1N1 D.3.1.1 viruses.

Today the WHO released their recommendations for the composition of this fall's 2026-2027 Northern Hemisphere flu vaccine, which recommends updates for all 3 flu strains; H1N1, H3N2, and Influenza B.

Overview

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

Egg-based vaccines

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

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

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


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

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

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

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

The 2026 Southern Hemisphere vaccine already has the recommended updated H1N1 component, but retains older strains against H3N2 and Influenza B. Despite this apparent mismatch, it will still likely provide important protection against severe disease.

Sadly, seasonal flu vaccine uptake in the United States peaked in 2019, and has begun a slow, but steady decline since.

Pandemic fatigue, plus growing anti-vaccination sentiment, and admittedly `hit-or-miss' protection against influenza infection have all had an impact.  

But the more we learn about influenzas' extrapulmonary impacts on the body (see Risk of Cardiovascular Events After Influenza: A Population-based Self Controlled Case Series Study), the more important protecting yourself becomes.

Which is why I consider the flu vaccine to be an important part of my `flu prevention' strategy each year (along with masking, handwashing, and avoiding indoor crowds).    

While none of this guarantees I'll continue to go unscathed, my last bout with `flu' was in the summer of 2009 (after attending a pandemic flu conference!), and I've only contracted COVID once, before the first vaccine was released.

Since my strategy seems to work, I see no reason to `fix' it. 

South Korea: MAFRA Extends Special Quarantine Period for 3rd Month (to March 31st)

 

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On January 5th, South Korea ordered Special Quarantine Measures Implemented for one Month to Prevent the Spread of HPAI, which was extended in early February due to concurrent outbreaks of FMD and ASF along with ongoing HPAI.

Over the past 3 weeks the number of ASF outbreaks has more than tripled (from 6 to 20), and more than a dozen HPAI outbreaks have been reported in poultry.  

As noted on Wednesday, a new subtype (H5N9) has been increasingly reported in South Korea, and MAFRA has already ordered their third 24-hour halt in the transport of livestock (poultry, ducks, and pigs) this week.

Today, MAFRA published an extraordinary (14.5 mb) collection of 132 maps and aerial photos (see sample below), of migratory bird arrival areas where livestock-related vehicles and workers are restricted from entering.

Given that the northbound phase of Korea's migratory bird season begins in early March - and often extends into May - this may not be the last extension to this special quarantine period we see. 

Some (translated) excerpts from today's announcement follow:

The special quarantine period for livestock infectious diseases has been extended until March, and all-out measures are being taken to prevent further outbreaks.

February 27, 2026, 3:44 PM, Quarantine Policy Bureau 

The Central Disaster and Safety Countermeasures Headquarters ( Director Song Mei-ryeong, Minister of Agriculture, Food and Rural Affairs , hereinafter referred to as the Central Disaster and Safety Countermeasures Headquarters ) for Livestock Infectious Diseases ( Highly Pathogenic Avian Influenza , Foot - and-Mouth Disease, African Swine Fever ) announced that considering the current risk of additional outbreaks of livestock infectious diseases, the existing special quarantine period (October 1, 2025 - February 28, 2026) will be extended by one month until March 31 ( Friday ) to strengthen quarantine management .

1. Highly pathogenic avian influenza (AI)

< Occurrence situation and situation diagnosis >

This winter ('25/'26 season ) , there have been 50 cases of highly pathogenic avian influenza in poultry farms and 59 cases in wild birds .

* Poultry farm occurrence status ( total 50 cases ): 11 cases in Gyeonggi , 9 in North Chungcheong , 9 in South Chungcheong , 4 in North Jeolla , 10 in South Jeolla , 4 in North Gyeongsang , 1 in South Gyeongsang , 1 in Gwangju , 1 in Sejong

** Status of wild bird detection ( total 59 cases ): Gyeonggi 6 , Gangwon 6, Chungbuk 1, Chungnam 14, Jeollabuk-do 6, Jeollanam-do 7 , Gyeongbuk 3, Gyeongnam 5, Jeju 4, Seoul 3, Busan 2, Incheon 1, Gwangju 1

In our country, highly pathogenic avian influenza first occurred in a poultry farm (September 12, 2025) 47 days earlier than the previous 24/25 season (October 29, 2024) during this 25/26 winter season . The outbreak area has also expanded significantly ( from 26 cities and counties to 29 ) compared to last season . In addition , the number of detections in wild birds has increased from 43 to 59 , and the detection area has expanded nationwide (from 30 cities and counties to 38 ) . Therefore, it is necessary to strengthen quarantine management, such as thorough disinfection and access control, more than ever before .

The Central Disaster and Safety Countermeasure Headquarters assessed that there is a risk of additional outbreaks considering that the results of the February migratory bird population survey showed that there were 1.33 million birds * , a large number of birds inhabiting the area , and that highly pathogenic avian influenza continued to occur in domestic poultry farms and wild birds in February as well as sporadic outbreaks during the migratory bird migration period since March . Therefore , the main quarantine measures implemented during the special quarantine period will be extended until Tuesday, March 31 to continue strengthened quarantine management of poultry farms , etc.

* According to the February migratory bird habitat survey ( cooperation with the Ministry of Climate and Environment ), 1.33 million birds were confirmed , a 1.2% decrease in the number of birds compared to the previous month (1.35 million ) , but many migratory birds still live across the country.

* * Farm (50 cases ) : (September ) 1 case → (October ) 1 case → (November ) 4 cases → (December ) 22 cases → (January ) 10 cases → (February ) 12 cases

Migratory birds (59 cases ): (September ) 0 cases → (October ) 2 cases → (November ) 11 cases → (December ) 10 cases → ( January ) 19 cases → ( February ) 17 cases

*** Occurrences in the past March to May : ('23 ) 2 cases in March , 4 cases in April , ( '24 ) 1 case in May , ( '25 ) 8 cases in March , 4 cases in April

< Strengthened quarantine measures >

To prevent further sporadic outbreaks due to migratory birds moving north, the Central Disaster and Safety Countermeasure Headquarters will strengthen quarantine measures as follows until Tuesday , March 31 .

First , we will continue to operate the Central Disaster and Safety Countermeasures Headquarters for Highly Pathogenic Avian Influenza system , cooperate with relevant ministries such as the Ministry of the Interior and Safety and the Ministry of Climate Change to respond with all-out efforts across the government , and all local governments will continue to operate response headquarters and situation rooms .

Second , a special quarantine inspection will be conducted jointly by the Ministry of Agriculture, Food and Rural Affairs, the Ministry of the Interior and Safety, and other relevant organizations in 32 cities and counties at risk during the northern migration period of migratory birds (March 3 to March 17) , and a ' Quarantine Strengthening Public Relations Campaign ' will be promoted together with producer groups to improve quarantine rules for poultry farms . *

* Major farm initiatives for the month of March : ① Changing boots when entering and exiting the barn , ② General cleaning and disinfection , ③ General rat extermination work

Third , to prevent further outbreaks in laying hens, one-on-one dedicated managers will be assigned to laying hens in farms with more than 50,000 hens nationwide by March to manage vehicles and people entering and exiting the farms . In particular, control posts installed in densely populated areas and large-scale laying hens with more than 200,000 hens will be intensively inspected to ensure compliance with quarantine measures such as vehicle disinfection .

* In addition, random environmental inspections will be conducted on hazardous livestock vehicles ( egg , manure , feed transport ) and goods entering and exiting laying hen farms nationwide during March .

Fourth , the existing administrative orders (11 cases) and public notices (7 cases) that have been issued and are in effect will be extended until March , and additional administrative orders ( 2 cases ) and public notices (3 cases ) will be issued and operated to prevent outbreaks at poultry farms .

* Additional measures : ① Restriction on partial shipment of laying hens nationwide for 2 weeks (March 1 to March 14), ② Restriction on the entry of laying hens into outbreak cities and counties for 2 weeks (March 1 to March 14), ③ Restriction on entry of livestock disposal personnel to other farms for purposes other than livestock disposal for 1 month (March 1 to March 31)

- However , shipment of all laying hens from a farm to a slaughterhouse is possible , and in cases where unavoidable circumstances are recognized , movement ( shipment ) is permitted under limited circumstances under the supervision of public officials. Administrative orders and public notices may be adjusted depending on the situation.

        (Continue . . .) 

This announcement also contains special instructions for dealing with ASF and FMD.   

In an update from last week's report on pig feed additives which tested positive for ASF DNA, we have the following update which also found ASF genes in on-farm stockpiled feed.

Once again, this appears to be via PCR, meaning that the infectiousness of this sample hasn't been ascertained. 

African swine fever (ASF) genes detected in compound feed made from plasma proteins, leading to strengthened quarantine measures to prevent its spread.

2026.02.24 23:00:00 Foot-and-Mouth Disease Prevention Division, Quarantine Policy Bureau

The African Swine Fever Central Disaster and Safety Countermeasures Headquarters ( Director Song Mei-ryeong, Minister of Agriculture, Food and Rural Affairs , hereinafter referred to as the Central Disaster and Safety Countermeasures Headquarters ) announced on Tuesday , February 24 that it will strengthen quarantine measures to prevent the spread of African swine fever (ASF) after the gene was detected in pig feed .

1. Detection circumstances

The Korea Centers for Disease Control and Prevention (KCDC) is conducting a comprehensive inspection ( carcasses and environmental samples ) on pig farms nationwide . During this process , a detailed inspection was conducted on carcasses and environmental samples such as feed from a pig farm (No. 1 ) in Hongseong, South Chungcheong Province , and on February 24 , it was announced that the African swine fever (ASF) gene was detected * in two cases ( same product ) of compound feed made from plasma protein .

* Results of testing by the Chungcheongnam-do Animal Hygiene Testing Laboratory and the Animal and Plant Quarantine Agency , positive result due to detection of ASF gene

2. Key quarantine measures

The central government will first order local governments across the country to order owners of feed* in which African swine fever (ASF) genes have been detected at pig farms to dispose of the relevant items in accordance with the Livestock Infectious Disease Prevention Act ** .

* It is assumed to have been manufactured using pig-derived plasma protein supplied by OOO Lab as the raw material.

** Article 23 of the Livestock Infectious Disease Prevention Act ( Incineration of Contaminated Materials, etc. )

In addition , for feed in which African swine fever (ASF) genes have been detected, the relevant companies ( some names ), production dates , and products will be disclosed on the Animal and Plant Quarantine Agency website (www.qia.go.kr) * , and local governments plan to recommend that pig farms nationwide stop using the relevant feed as a preventive measure .

 (Continue . . . )

While it may appear that South Korea's livestock disease woes are far greater than most other countries, it is worth mentioning that few countries are as open about their agricultural disease challenges and responses. 

So how much of an outlier South Korea really is, is difficult to say. 

But given the way that livestock diseases propagate around the globe, countries that are currently under less pressure may find their current status quos to be fleeting.  

California: Background on the Outbreak of H5N1 in Elephant Seals at Año Nuevo Natural Reserve

 
California Parks

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Yesterday, California Parks and UC Santa Cruz announced the first U.S. detection of H5N1 in Elephant Seals at the Año Nuevo Natural Reserve (see FluTracker's thread) after dozens of seals  were observed either sick or dying  and the virus was confirmed (on Tuesday night) by the USDA’s NVSL lab. 

(Excerpt)

On Feb. 19 and 20, Beltran’s team noticed seals at Año Nuevo Reserve with abnormal respiratory and neurological signs, including weakness and tremors. They collected samples from sick and dead elephant seals and took them to UC Davis for testing at the California Animal Health and Food Safety Laboratory System. Initial screening revealed the samples were positive for avian influenza, which the USDA’s NVSL lab now confirms is HPAI H5N1.

While the details of this outbreak have already been well covered by the media, this is just the latest in a series of concerning HPAI spillovers into marine mammals around the globe.

We've repeatedly looked at the devastation of colonies of pinnipeds (seals, sea lions, walruses) in South America, and elsewhere, due to this virus. 

Although exact numbers are impossible to ascertain, a little over a year ago in Nature Reviews: The Threat of Avian Influenza H5N1 Looms Over Global Biodiversity, we saw the following proffered butcher's bill.

An estimated half a billion domestic fowl have died of H5N1 (ref. 4), and this number is rising; mortality in wildlife is more difficult to quantify than in poultry, but the effects are substantial. By mid-2024, H5N1 infections were documented in at least 406 bird and 51 mammal wild species (according to reports on the World Animal Health Information System (WAHIS)), and available reports suggest that multiple millions of wild animal individuals may have died (Fig. 1a).

The most noteworthy mass-mortality events include more than 200,000 wild birds in coastal areas of Peru6; 24,000 sea lions in South America7; 20,500 wild birds in Scotland8; 6,500 Cape cormorants in Namibia9; and 17,400 elephant seals, including >95% of the pups in Argentina10. These figures, however, largely underestimate actual mortalities, owing to a pervasive lack of monitoring, testing and reporting — particularly in inaccessible areas and in disadvantaged countries4,7.

While North America has seen occasional spillovers of HPAI H5 into marine mammals (primarily seals & dolphins see here, here, and here), they pale in comparison to what has been reported from South America, and have never included elephant seals until now.

(Note: Those will long memories will recall that in 2013 - in The 2009 H1N1 Virus Expands Its Host Range (Again) - we looked at a US Davis study which found that the 2009 H1N1 pandemic influenza virus had managed to jump to elephant seals as early as 2010.)

All of this is a concern - because while H5N1 hasn't managed to figure out how to transmit efficiently from human-to-human - there is growing evidence to suggest it may be close to doing so in marine mammals.  

• Two years ago, in a research letter (see EID Journal: HPAI A(H5N1) Viruses from Multispecies Outbreak, Argentina, August 2023), researchers wrote: ". . . it seems likely that pinniped-to-pinniped transmission played a role in the spread of the mammal-adapted HPAI H5N1 viruses in the region . . ."

• In the summer of 2024, we looked at a Preprint: Massive outbreak of Influenza A H5N1 in elephant seals at Peninsula Valdes, Argentina: increased evidence for mammal-to-mammal transmission

• A year ago, we looked at Preprint: Pathology of Influenza A (H5N1) Infection in Pinnipeds Reveals Novel Tissue Tropism and Vertical Transmission.

• And last March, in Nature Comms: Cross-species and mammal-to-mammal transmission of clade 2.3.4.4b HPAI A/H5N1 with PB2 adaptations, the authors wrote:

• Several mutations were detected months later in sea lions in the Atlantic coast, indicating that the pinniped outbreaks on the west and east coasts of South America are genetically linked. These data support sustained mammal-to-mammal transmission of HPAIV in marine mammals over thousands of kilometers of Chile’s Pacific coastline, which subsequently continued through the Atlantic coastline.

Although H5N1 remains predominantly an avian adapted virus, over the past 5 years is has become increasingly `mammalian friendly'.  Dairy cows, domestic cats, and peridomestic animals like mice, skunk, and foxes have all been greatly affected, and each spillover is another opportunity for the virus to test out new combinations of mammalian adaptations. 

Last September, in ISIRV: Update on H5N1 Panzootic: Infected Mammal Species Increase by Almost 50% in Just Over a Year we looked yet at another concerning milestone for the H5 virus. 

And just last month, in Adv. Genetics (Review Article) : Evolution of H5N1 Cross‐Species Transmission - Adaptive Mutations Driving Avian‐to‐Human Infection, we looked at another cautionary report that warned of the dangers of mammalian spread.

 

These types of reports have become so common, that events that would have inspired screaming headlines 3 or 4 years ago are scarcely noticed today (see Avian Flu's New Normal: When the Extraordinary Becomes Ordinary).

While hopefully this spillover to elephant seals in California won't lead to the kind of carnage we've seen in South America, this should be a sobering reminder that while we continue to dither in our response to H5N1, it continues to explore new ways to expand its geographic and host ranges. 

And, for now at least, H5Nx seems to be on a roll. 

South Korea: H5N9 Rising

 

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Last last year, South Korea's MAFRA Reported Increased Infectivity & Pathogenicity of This Year's Avian Flu Strains, which - for the first time - included 3 HPAI strains (H5N1, H5N6, and H5N9). 

Of particular concern, their Animal and Plant Quarantine Agency conducted an evaluation of the infectivity and pathogenicity of the highly pathogenic avian influenza virus ( serotype H5N1) and found that the infectivity was more than 10 times higher than in previous years .

While we've been watching subtypes other than H5N1 (H5N6 & H5N5 in particular) around the world, HPAI H5N9 has been comparatively rare. 

• A little over a year ago, California Reported a New H5N9 Reassortant In Ducks, but that appears to have been a one-off event. 

• Last May, the Philippines DOA Reports Their 1st Detection of HPAI H5N9

But as the following WOAH WAHIS report illustrates, global reports have been limited (4 HPAI, 1 LPAI) since 2017:

In early February, however, South Korea reported 3 poultry farm outbreaks (starting in Dec 2025) to WOAH resulting in the culling/loss of 150K birds. 

• ob_181082 - Donggok-ri, Dasi-myeon, Naju-si, Jeollanam-do, Republic of Korea
• ob_181085 - Omani-gil, Cheonbuk-myeon, Boryeong-si, Chungcheongnam-do, 33403, Republic of Korea
• ob_181080 - Jinjuk-ri, Cheongso-myeon, Boryeong-si, Chungcheongnam-do, Republic of Korea

While we haven't seen any new updates posted by WOAH, on February 6th MAFRA reported it would `. . . strengthen quarantine management following the confirmation of a case of highly pathogenic avian influenza (H5N9 type ) at a laying hen farm ( approximately 653,000 birds ) in Yesan, South Chungcheong Province.'

On February 11th , MAFRA warned:

The virus that occurred in domestic poultry farms this winter has a higher infectious power than in previous years, and in particular , in the case of the H5N9 type, symptoms such as death are not obvious in ducks , so the risk of transmission is higher than ever , so local governments, related organizations , and poultry farms across the country must thoroughly implement quarantine measures, 

Yesterday Hong Kong announced the suspension of imports of poultry meat and products (including poultry eggs) from Boryeong-si of Chungcheongnam-do Province in Korea due to a WOAH notification of an H5N9 outbreak, although it isn't clear if this is a new outbreak, or refers to the two from Dec/Jan.

Either way, this appears to be the first sustained spread of HPAI H5N9 in poultry reported anywhere in the world. 

Today, and for the 2nd time in 3 days, South Korea has ordered a 24-hour halt in the movement of live poultry. as new outbreaks of (unspecified) HPAI H5 continue to mount.

South Korea is also dealing with FMD, and a rapidly escalating outbreak of ASF (African Swine Fever), which appears to be due to the sale and use of contaminated pig feed. 

It's a lot to contend with, even for a country like South Korea. 

The spring northbound bird migration begins in early March in South Korea, and runs through May, meaning avian flu activity could easily persist for several more months on the Korean peninsula.

The mild (or subclinical) spread of H5N9 in ducks is particularly problematic, as detection and eradication will be difficult. Long term infection could produce even more reassortants. 

While there are no known human infections with HPAI H5N9, we've seen human infection by other H5 subtypes; including H5N1, H5N2, H5N5, and H5N6 HPAI viruses.   

Since we've also seen novel flu viruses with an N9 neuraminidase spillover to humans (China's H7N9 virus 2013-2019), there is little reason to believe it would present much of a barrier for H5 viruses. 

The $64 question is whether this outbreak of H5N9 in South Korea virus is a flash in the pan, or if it has `legs'.

In 2016's Sci Repts.: Southward Autumn Migration Of Waterfowl Facilitates Transmission Of HPAI H5N1, we looked at a study which found that the flu viruses migratory birds encounter as they fly north in the spring often thrive - or reassort - in their summer high latitude roosting areas, and then are redistributed via the migratory flyways the following fall. 

This is likely how South Korea's disastrous January 2014 H5N8 outbreak made it to the United States and Europe in less than a year, and became globally dominant by 2016. 

A reminder that whatever avian viruses that may emerge South Korea - or any other country - assuming they are biologically `fit' enough, are unlikely to stay put for very long.