The World Health Organization has released its recommended composition for influenza vaccines to be used during the 2027 Southern Hemisphere influenza season, updating the viral strains that vaccine manufacturers and health authorities should target for the upcoming flu season.

The recommendations were announced after an international consultation that reviewed influenza surveillance, laboratory and epidemiological data collected from different parts of the world. WHO updates influenza vaccine recommendations twice each year because the viruses responsible for seasonal flu continually evolve.

Three Main Influenza Viruses Selected

For egg-based influenza vaccines, WHO recommends three virus components for the 2027 Southern Hemisphere season:

• A/Missouri/11/2025 (H1N1)pdm09-like virus
• A/Darwin/1454/2025 (H3N2)-like virus
• B/Tokyo/EIS13-175/2025 (B/Victoria lineage)-like virus

For cell-culture, recombinant-protein or nucleic-acid-based vaccines, WHO recommends the same H1N1 component but different H3N2 and B/Victoria lineage reference viruses.

The recommendations provide manufacturers with the viral targets needed to develop and produce vaccines ahead of the next Southern Hemisphere influenza season.

Why Vaccine Composition Changes

Influenza viruses constantly undergo genetic and antigenic changes.

As circulating viruses evolve, the strains that were dominant in an earlier season may not remain the most representative viruses for a future season.

For this reason, WHO’s Global Influenza Surveillance and Response System continuously collects information from countries and laboratories.

Experts then examine the characteristics of circulating viruses and compare them with available vaccine strains.

This process helps determine whether existing vaccine components remain appropriate or need to be replaced.

Global Surveillance Data Used

The latest recommendations were developed following a consultation held from 21 to 24 September 2026.

Experts reviewed global influenza activity, genetic and antigenic characteristics of circulating viruses, epidemiological information and vaccine-related data before determining the recommended composition.

The process involves WHO collaborating centres, national influenza laboratories, regulatory laboratories and other technical experts.

This international surveillance network allows information from different regions to be considered before the vaccine composition is finalized.

Influenza A Dominated Many Regions

WHO reported that between February and August 2026, influenza A(H1N1)pdm09, A(H3N2) and influenza B viruses circulated in varying proportions across all regions.

Influenza A viruses were the most common in most parts of the world.

However, influenza B viruses dominated in Northern and Western Africa, North America and Eastern Asia during the period reviewed.

The regional differences demonstrate why global surveillance is necessary when selecting vaccine components.

Importance for Southern Hemisphere Countries

The Southern Hemisphere influenza season includes countries across South America, southern Africa, Australia, New Zealand and other areas south of the equator.

National health authorities use WHO recommendations as an important reference when preparing seasonal vaccination programmes.

Vaccine manufacturers also rely on the recommendations when developing and producing vaccines for the upcoming season.

The objective is to ensure that vaccines are as closely matched as possible to viruses expected to circulate.

Monitoring Zoonotic Influenza

The WHO review also examined influenza viruses circulating among animals, particularly viruses that have infected humans.

Zoonotic influenza remains an important concern because some animal influenza viruses have the potential to cause human outbreaks and, under certain circumstances, develop into wider public-health threats.

The surveillance process therefore considers both seasonal human influenza and emerging zoonotic viruses.

WHO also reviews whether new candidate vaccine viruses should be developed for pandemic preparedness.

Vaccination Remains Important

Seasonal influenza causes substantial illness every year and can result in serious disease, hospitalization and death, particularly among vulnerable populations.

Regularly updating vaccine composition is therefore an important component of influenza prevention.

The effectiveness of vaccination can vary depending on several factors, including how closely vaccine viruses match circulating viruses and the characteristics of the people receiving vaccination.

Nevertheless, maintaining an updated vaccine supply remains a key part of seasonal influenza preparedness.

A Continuous Global Process

The latest recommendation is part of a long-running international surveillance process.

WHO has operated the Global Influenza Surveillance and Response System since 1952, creating one of the world’s longest-running international disease-surveillance networks.

The system allows countries and laboratories to share influenza information and supports the twice-yearly vaccine-composition process.

Preparing for the 2027 Season

The September 2026 recommendation now provides the basis for preparations for the 2027 Southern Hemisphere influenza season.

Regulators, manufacturers and public-health authorities can use the recommended viral composition to plan vaccine production and immunization programmes.

The process also demonstrates how international disease surveillance can directly influence vaccine development.

As influenza viruses continue to evolve, WHO’s regular monitoring and vaccine updates will remain an important part of global preparedness against seasonal influenza and potential emerging influenza threats.