The World Health Organization (WHO) has announced its recommendations for the viral composition of influenza vaccines for the 2026–2027 northern hemisphere flu season, following a four-day consultation that reviewed global influenza surveillance data. Because influenza viruses constantly evolve, vaccine formulations must be regularly updated to ensure they remain effective. WHO’s recommendations guide national regulatory authorities and vaccine manufacturers worldwide in developing, producing, and licensing vaccines tailored to the strains most likely to circulate, helping to reduce severe illness and deaths.
These consultations are held twice a year—once for each hemisphere—and bring together experts from WHO Collaborating Centres and Essential Regulatory Laboratories within the Global Influenza Surveillance and Response System (GISRS). Specialists analyze data collected year-round through GISRS and its partners. WHO Director-General Dr Tedros Adhanom Ghebreyesus emphasized that the ongoing global collaboration under GISRS enables vaccines to be updated in response to emerging strains, strengthening protection for communities worldwide.
During the most recent influenza season, a notably different A(H3N2) variant, classified as J.2.4.1 or “subclade K,” emerged in August 2025 and spread rapidly across countries. This variant contributed to an earlier-than-usual start to the influenza season in many areas and was responsible for the majority of reported cases globally. Influenza A viruses were predominant overall, including other A(H3N2) and A(H1N1) variants. Influenza B viruses of the B/Victoria lineage were detected at low levels, while no B/Yamagata lineage viruses have been reported since March 2020.
Experts also assessed zoonotic influenza viruses circulating in animals that have infected humans, given their pandemic potential. Since late September 2025, 25 human infections with zoonotic influenza have been reported from six countries. Most cases involved exposure to infected animals or contaminated environments, with no evidence of human-to-human transmission. As part of pandemic preparedness efforts, specialists recommended developing a new candidate vaccine virus for an A(H9N2) strain to enable rapid vaccine production if needed.
For the 2026–2027 northern hemisphere season, WHO recommended specific virus strains for different types of vaccines. Egg-based vaccines should include A/Missouri/11/2025 (H1N1)pdm09-like, A/Darwin/1454/2025 (H3N2)-like, and B/Tokyo/EIS13-175/2025 (B/Victoria lineage)-like viruses. Cell culture-, recombinant protein-, or nucleic acid-based vaccines should contain A/Missouri/11/2025 (H1N1)pdm09-like, A/Darwin/1415/2025 (H3N2)-like, and B/Pennsylvania/14/2025 (B/Victoria lineage)-like viruses.
Seasonal influenza is a widespread acute respiratory infection, causing an estimated one billion cases annually, including three to five million severe cases. It is responsible for between 290,000 and 650,000 respiratory deaths each year. Since 1952, WHO’s GISRS has served as the world’s longest-running global disease surveillance platform, underpinning efforts to monitor influenza trends and inform vaccine development.
