There have been no confirmed detections of infections caused by a family of flu viruses known as Influenza B/Yamagata since March 2020, suggesting it may have been eliminated. Based on that, the World Health Organization recommends leaving it out of flu shot compositions for next year.
"It is unlikely that B/Yamagata-lineage viruses are circulating in the population. Therefore, it is the opinion of the WHO influenza vaccine composition advisory committee that the inclusion of B/Yamagata-lineage antigens in influenza vaccines is no longer warranted," the agency said when it released its recommendations for 2024 flu vaccines Sept. 29.
Instead, the WHO is recommending a trivalent vaccine for the 2024 Southern Hemisphere flu season that should target two influenza A viruses — H1N1 and H3N2 — and an influenza B/Victoria virus.
Vaccines for the current flu season in the U.S. still include a Yamagata lineage virus.