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Following FDA Guidance, CSL Seqirus to Remove B/Yamagata Influenza Virus Strain from Portfolio of Influenza Vaccines for the 2024/25 U.S. Season


The U.S. Food and Drug Administration (FDA), in collaboration with the World Health Organization (WHO), has directed influenza vaccine manufacturers to remove the B/Yamagata influenza virus strain from all influenza vaccines distributed in the United States, as soon as possible, preferably by the 2024/25 influenza season.1 

As a global leader in the protection of public health, CSL Seqirus worked closely with the FDA during 2023 to align on a path forward and is fully prepared to meet the FDA’s directive by bringing our complete portfolio of seasonal influenza vaccines to the U.S. market in trivalent formulations for the 2024/25 influenza season. Across the world, we are collaborating with regulatory bodies and public health authorities on an appropriate timeline for each country. 

“Influenza continues to cause significant public health burden and the agility to rapidly adapt vaccines to match the circulating strains remains paramount. We are proud to say that we have responded swiftly to meet the FDA’s directive and are committed to working with health authorities to support this transition ahead of the 2024/25 flu season,” said Gregg Sylvester, Chief Health Officer and Head of Medical Affairs, CSL Seqirus. “Over the past two flu seasons, we have seen an alarming decline in influenza vaccination rates. In addition to implementing this change, we strive to increase immunization rates and vaccine confidence.”

A decline in B/Yamagata circulation was detected before the onset of the COVID-19 pandemic by the WHO’s global influenza response and surveillance system, which has subsequently confirmed no circulation of B/Yamagata lineage viruses since March of 2020. Given this, the FDA has strongly recommended the removal of the B/Yamagata antigen from seasonal influenza vaccines in the U.S. as soon as possible.

The disappearance of B/Yamagata is a testament to the critical role of widely implemented influenza immunization programs, amongst other contributing factors such as the inherent characteristics and epidemiology of the B/Yamagata virus and the unique environment created by the COVID-19 pandemic.2



Food and Drug Administration. Center for Biologics Evaluation and Research. 183rd Vaccines and Related Biological Products Advisory Committee. Summary Minutes. October 2023.
Koutsakos, M., Wheatley, A. K., Laurie, K., Kent, S. J., & Rockman, S. (2021). Influenza lineage extinction during the COVID-19 pandemic? Nature Reviews Microbiology, 19(12), 741-742.