The World Health Organization has announced the recommended composition of influenza vaccines for the 2027 Southern Hemisphere influenza season, updating the virus strains that manufacturers should use in seasonal flu vaccines.
The recommendations were issued on September 25, 2026, following a four-day international consultation involving WHO collaborating centres, national influenza laboratories, regulatory laboratories and other experts.
The update reflects changes in influenza viruses circulating around the world and is part of WHO’s twice-yearly process for keeping seasonal vaccines aligned with the viruses most likely to cause illness.
WHO recommends three main influenza components
For egg-based vaccines intended for the 2027 Southern Hemisphere season, WHO recommends viruses representing:
- A/Missouri/11/2025-like H1N1pdm09
- A/Darwin/1454/2025-like H3N2
- B/Tokyo/EIS13-175/2025-like virus from the B/Victoria lineage.
For cell culture, recombinant protein or nucleic-acid-based vaccines, WHO recommends:
- A/Missouri/11/2025-like H1N1pdm09
- A/Darwin/1415/2025-like H3N2
- B/Pennsylvania/14/2025-like virus from the B/Victoria lineage.
The differences between the egg-based and non-egg-based formulations reflect the way influenza viruses can behave differently when grown in different production systems.
Why influenza vaccines are updated
Influenza viruses continually evolve.
As viruses change genetically and antigenically, the viruses circulating in populations can become less closely matched to strains used in previous vaccine formulations.
WHO therefore reviews influenza surveillance data twice a year.
The Southern Hemisphere recommendations are normally issued in September, while recommendations for the Northern Hemisphere are issued in February.
The recommendations are then used by national regulatory authorities and vaccine manufacturers as they develop, produce and license seasonal influenza vaccines.
Global surveillance drives the decision
The September consultation examined influenza viruses detected between different regions and populations.
WHO said that from February through August 2026, influenza A(H1N1)pdm09, A(H3N2) and influenza B viruses circulated in varying proportions across all regions and caused disease.
Influenza A viruses were the most common in most regions during that period.
However, WHO reported that influenza B viruses predominated in Northern and Western Africa, North America and Eastern Asia.
That regional variation is one reason a single global influenza picture cannot fully describe which viruses are circulating in individual countries.
WHO’s surveillance network monitors changing viruses
The recommendations rely heavily on the WHO Global Influenza Surveillance and Response System, known as GISRS.
GISRS has operated for decades and brings together national influenza centres, WHO collaborating centres, regulatory laboratories and other participating institutions.
The system collects information about circulating influenza viruses and their genetic and antigenic characteristics.
WHO uses this information to assess whether existing vaccine viruses remain appropriate and whether new candidate vaccine viruses are needed.
The 2027 recommendation is not a prediction of disease severity
The selection of vaccine strains should not be interpreted as a prediction that the 2027 influenza season will be more severe than the 2026 season.
WHO’s process is primarily about matching vaccines to the viruses expected to circulate.
A change in the recommended composition does not by itself establish how many people will become infected, how severe the season will be or how many hospitalisations will occur.
Those outcomes depend on multiple factors, including virus characteristics, population immunity, vaccination coverage, age distribution and healthcare access.
H1N1 and H3N2 remain part of the formulation
The recommended 2027 Southern Hemisphere vaccines continue to include influenza A(H1N1)pdm09 and A(H3N2) components.
Both are established seasonal influenza virus groups that have been monitored extensively through international surveillance.
WHO’s recommendation for 2027 uses newly selected representative viruses for these components.
The inclusion of these components reflects continued circulation and the need to maintain protection against relevant influenza A viruses.
B/Victoria lineage remains the influenza B component
WHO’s 2027 recommendations also include an influenza B virus from the B/Victoria lineage.
The recommended B/Victoria component differs according to the vaccine production platform.
For egg-based vaccines, WHO recommends a B/Tokyo/EIS13-175/2025-like virus.
For cell culture, recombinant protein or nucleic-acid-based vaccines, it recommends a B/Pennsylvania/14/2025-like virus.
Both are intended to represent the B/Victoria lineage.
The B/Yamagata lineage remains absent
WHO has continued its transition away from including a B/Yamagata component in seasonal influenza vaccines.
The organisation’s previous recommendations had already concluded that inclusion of a B/Yamagata lineage antigen was no longer warranted because of the lack of recent detections in human surveillance.
The 2027 Southern Hemisphere recommendation contains H1N1pdm09, H3N2 and B/Victoria components and does not add a B/Yamagata component.
This continues the move toward trivalent seasonal influenza vaccines.
Vaccine manufacturers now use the recommendations
WHO’s recommendations are an important stage in the seasonal vaccine production cycle.
Manufacturers use recommended viruses and associated candidate vaccine viruses to develop vaccine products for the coming season.
WHO has also published candidate vaccine viruses and potency-testing reagents for the 2027 Southern Hemisphere season. These include candidate viruses for H1N1pdm09, H3N2 and B/Victoria.
National regulators subsequently determine which vaccine products can be licensed and used within their respective countries.
Countries make their own regulatory decisions
WHO’s recommendations do not constitute automatic approval of a vaccine in every country.
National or regional regulatory authorities are responsible for approving vaccine compositions and products for use in their jurisdictions.
National public-health authorities also determine how influenza vaccination is recommended and delivered to their populations.
WHO’s role is to provide the scientific recommendations that inform this process.
This distinction is important because vaccine availability, licensing and vaccination policies can differ between countries.
Southern Hemisphere countries prepare for the next season
The recommendations are particularly relevant to countries that use Southern Hemisphere influenza vaccine formulations.
The Southern Hemisphere includes countries in Africa, South America, Oceania and parts of Asia.
The timing of influenza seasons varies by geography, and tropical countries can experience influenza circulation throughout the year.
WHO therefore provides guidance for countries and regions that need to determine which formulation is most appropriate for their epidemiological circumstances.
Africa has a specific role in the surveillance picture
WHO’s surveillance data show that influenza circulation can differ significantly across African regions.
The organisation reported that influenza B predominated in Northern and Western Africa during the February-August period used for the latest vaccine assessment.
This does not mean every country in those regions had the same influenza pattern.
National surveillance remains important because vaccine policy and disease patterns can differ between neighbouring countries.
For countries such as Nigeria, national health authorities therefore need to consider both WHO recommendations and local surveillance when making vaccination decisions.
The process also monitors pandemic threats
The September consultation was not limited to ordinary seasonal influenza.
Experts also reviewed recent A(H5) and other zoonotic influenza viruses and considered whether new candidate vaccine viruses were needed for pandemic preparedness.
This is separate from the selection of seasonal vaccine components.
Zoonotic influenza viruses can infect animals and, in some circumstances, humans. Their surveillance helps authorities identify viruses that could potentially pose wider public-health risks.
WHO has said a summary of zoonotic influenza viruses and candidate vaccine-virus updates from the consultation will be published separately.
The recommendations are based on months of data
The September decision was not based on a single outbreak or a single country’s surveillance results.
WHO’s expert consultation reviewed global influenza activity, virus genetic and antigenic characteristics and results from vaccine-related studies.
This broad evidence base allows experts to compare viruses circulating in different parts of the world.
The process is repeated because influenza viruses can continue to evolve after the recommendation has been made.
What the new recommendation means for the public
For the public, the most important point is that seasonal influenza vaccines are periodically updated.
The purpose is to keep vaccine composition aligned as closely as possible with circulating influenza viruses.
However, the strain recommendation does not guarantee that vaccination will prevent every influenza infection.
Vaccine effectiveness varies between seasons and populations and can be affected by the match between vaccine viruses and circulating viruses, as well as individual and population factors.
WHO’s recommendations are therefore part of a wider influenza-control strategy that includes surveillance, vaccination and public-health preparedness.
What happens next
Following WHO’s September recommendation, manufacturers can proceed with development and production of vaccines for the 2027 Southern Hemisphere season using the recommended virus compositions and candidate vaccine viruses.
National regulators will then handle licensing and other regulatory processes.
WHO’s Global Influenza Surveillance and Response System will continue monitoring viruses as they circulate, meaning that surveillance does not stop after the September recommendation.
The organisation will also issue its next Northern Hemisphere vaccine composition recommendation in February 2027 as part of its regular annual cycle.
WHO updates vaccine composition for 2027
As of September 27, 2026, WHO has recommended updated influenza vaccine compositions for the 2027 Southern Hemisphere season, using H1N1pdm09, H3N2 and B/Victoria lineage viruses.
The recommendation follows a global surveillance and expert-review process conducted from September 21 to 24.
The update does not predict how severe the next influenza season will be. Instead, it provides manufacturers and national authorities with the scientific basis for developing and regulating seasonal vaccines for the coming Southern Hemisphere season.
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