2026–2027 Influenza Research Targets Updated: WHO Announces Recommended Vaccine Strains for the Northern Hemisphere

1.1 Rapid turnover of dominant variants

In August 2025, the A(H3N2) J.2.4.1 clade (the “K subclade”) was first detected. This strain exhibited significant antigenic differences from previous circulating viruses and quickly spread worldwide, becoming the dominant strain of the season. This rapid spread led to earlier-than-usual influenza activity and higher intensity compared to previous years.

1.2 Clear lineage patterns

Influenza A viruses predominated this season. In addition to the dominant K subclade, other A(H3N2) and A(H1N1)pdm09 variants were detected. Influenza B activity remained low, with only the B/Victoria lineage observed; the B/Yamagata lineage has not been reported globally since March 2020.

1.3 Continued zoonotic influenza risk

Between September 23, 2025, and the latest composition consultation, WHO received reports of 25 human infections with animal influenza viruses across six countries. All cases had documented exposure to infected animals or contaminated environments, with no evidence of sustained human-to-human transmission.

2.1 2026–2027 Northern Hemisphere Influenza Vaccine Composition

Figure 1: 2026–2027 Northern Hemisphere Influenza Vaccine Composition

2.2 Priority Research Directions

WHO experts emphasize the development of candidate vaccines against the H9N2 influenza A virus, which poses zoonotic transmission risks and potential pandemic threats. This strain represents a core target for studies on cross-species transmission mechanisms, broad-spectrum vaccine development, and pandemic preparedness.