WHO Finalizes 2026-27 Northern Hemisphere Flu Vaccine Strains

The World Health Organization has issued recommendations on which influenza virus strains should be included in vaccines for the 2026-2027 northern hemisphere flu season. The guidance is intended to help national regulatory agencies and vaccine manufacturers align products with viruses expected to circulate.

Officials said the recommendations draw on global influenza surveillance data. They noted that vaccine strain selection needs regular revision because influenza viruses change over time, and closer matching is intended to improve protection.

Global surveillance points to a new A(H3N2) variant

Experts identified a new A(H3N2) variant classified as J.2.4.1 (subclade K). According to the WHO, it emerged in August 2025 and later spread worldwide.

The WHO said this variant contributed to an earlier and more active influenza season in several regions. Influenza A viruses were reported as the dominant type, with both A(H3N2) and A(H1N1) variants circulating.

Influenza B remains limited; B/Yamagata still absent

Surveillance detected low levels of influenza B viruses from the B/Victoria lineage. The WHO said no B/Yamagata lineage cases have been reported since March 2020.

The organization said the ongoing absence of B/Yamagata in reported surveillance is part of the evidence base considered when advising on vaccine composition, alongside the broader pattern of circulating influenza A and B viruses.

Zoonotic infections reported, with no sustained spread

Since September 2025, 25 human infections with zoonotic influenza have been reported from six countries, the WHO said. Officials said the cases were mainly linked to exposure to infected animals or contaminated environments.

The WHO said there was no evidence of human-to-human transmission in these reports. It added that monitoring such infections remains important because animal-origin influenza viruses can pose risks if they adapt to spread efficiently among people.

Candidate vaccine virus recommended for A(H9N2)

Separately, the WHO recommended developing a new candidate vaccine virus for an A(H9N2) virus. The organization said such a candidate could support rapid vaccine manufacturing if a pandemic threat were to emerge.

The WHO’s recommendations are advisory and are used by countries and companies as they make decisions on vaccine formulation and production. The organization did not specify how national regulators will implement the guidance, and vaccine availability and timing can vary by market.