On Sept. 25, 2026, the World Health Organization (WHO) announced its recommendations for the viral composition of influenza (or ‘flu’) vaccines for use in the 2027 southern hemisphere influenza season. The announcement was made following an international consultation on the composition of influenza virus vaccines.

Seasonal influenza causes substantial illness and many hospitalizations each year. Regular updates to vaccine composition are needed because influenza viruses continually evolve. WHO’s recommendations are used by national vaccine regulatory agencies and pharmaceutical companies around the world to develop, produce, and license influenza vaccines for the following influenza season. This ensures that vaccines are closely matched to the viruses expected to circulate, offering the best possible protection against severe illness and death.

Twice each year, WHO convenes experts from its Collaborating Centres and Essential Regulatory Laboratories to review surveillance data generated through the Global Influenza Surveillance and Response System (GISRS) and other sources, and recommend vaccine compositions for upcoming influenza seasons.

From February to August 2026, influenza A(H1N1)pdm09, A(H3N2) and influenza B viruses circulated in varying proportions across all regions of the world, causing disease. Influenza A viruses were the most common in most regions, except Northern and Western Africa, North America and Eastern Asia, where influenza B viruses dominated.

WHO recommends that vaccines for use in the 2027 southern hemisphere influenza season contain 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.

As part of the review, experts also looked at influenza viruses circulating in animals, particularly those that have caused infections in humans. These animal or zoonotic influenza viruses remain a significant concern because of their potential to cause pandemics.

These biannual meetings include a detailed assessment of these viruses and the selection of new candidate vaccine viruses (CVVs) from contemporary zoonotic influenza viruses, which can be used rapidly to manufacture vaccines should a pandemic threat arise.