The World Health Organization (WHO) has issued its recommendations for the viral composition of influenza (flu) vaccines for the 2026-2027 northern hemisphere season. These annual updates are crucial, ensuring vaccines are closely matched to expected circulating viruses to provide robust protection against severe illness and mortality. The recommendations were formulated following a four-day consultation that involved the analysis of global influenza surveillance data.
Global Collaboration in Vaccine Formulation
Influenza viruses undergo continuous evolution, necessitating regular updates to vaccine composition. The WHO's recommendations serve as guidance for national vaccine regulatory agencies and pharmaceutical companies globally in the development, production, and licensing of influenza vaccines.
These biannual consultations, which cover both northern and southern hemispheres, bring together experts from WHO Collaborating Centres and Essential Regulatory Laboratories. These specialists review and analyze data generated by the WHO Global Influenza Surveillance and Response System (GISRS) and its partners. WHO Director-General Dr. Tedros Adhanom Ghebreyesus emphasized the global nature of evolving influenza viruses and the continuous efforts of GISRS in updating vaccine strains to enhance community protection.
Recent Global Influenza Activity
In August 2025, a distinct A(H3N2) virus variant, classified as J.2.4.1 or "subclade K," emerged and circulated rapidly worldwide. This variant contributed to an earlier onset of the influenza season in multiple countries, with several reporting elevated activity levels, and accounted for the majority of reported influenza viruses across various regions.
Overall, influenza A viruses, including other variants of A(H3N2) and A(H1N1), were predominant during this period. Low levels of influenza B viruses (B/Victoria lineage) were detected, while no B/Yamagata lineage viruses have been reported since March 2020.
Vigilance Against Zoonotic Threats
Experts also examined influenza viruses originating in animals that have caused human infections. These zoonotic influenza viruses are considered a concern due to their potential to cause pandemics. Since September 23, 2025, 25 human infections with zoonotic influenza have been reported to the WHO from six countries. Most of these cases were linked to exposure to infected animals or contaminated environments, with no reported human-to-human transmission.
During the consultation, experts recommended developing a new candidate vaccine virus (CVV) for an A(H9N2) virus. This measure would facilitate rapid manufacturing should a pandemic threat involving an A(H9N2) virus emerge.
2026-2027 Northern Hemisphere Vaccine Recommendations
For vaccines intended for use in the 2026-2027 northern hemisphere influenza season, the WHO recommends the following compositions:
For Egg-Based Vaccines:
- An A/Missouri/11/2025 (H1N1)pdm09-like virus.
- An A/Darwin/1454/2025 (H3N2)-like virus.
- A B/Tokyo/EIS13-175/2025 (B/Victoria lineage)-like virus.
For 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.
- A B/Pennsylvania/14/2025 (B/Victoria lineage)-like virus.
The Global Burden of Seasonal Influenza
Seasonal influenza, an acute respiratory infection caused by influenza viruses, is prevalent globally. It leads to an estimated one billion cases annually, including 3–5 million severe cases, and is associated with approximately 290,000 to 650,000 respiratory deaths each year.