On March 5, 2024, the FDA’s Vaccines and Related Biological Products Advisory Committee (VRBPAC) decided that the B/Yamagata lineage of influenza viruses will not be included in the formulations for next winter’s flu vaccine.
“In the interest of public health, [the] FDA strongly recommended to influenza vaccine manufacturers the removal of the B/Yamagata lineage virus from seasonal influenza vaccines in the U.S. for the 2024-2025 influenza season,” the FDA stated in a release.
This decision was in response to the fact that B/Yamagata has not been detected since the beginning of the COVID-19 pandemic in March 2020. The seeming elimination of this strain from general circulation is unexplained, but public health officials hypothesized that the B/Yamagata lineage of the influenza virus had characteristics that likely contributed to its extinction, including an inability to mutate as quickly as other influenza strains, a propensity to infect adults older than 25 years, and more frequent occurrence in temperate climates.
What is certain about the 2024-2025 influenza vaccine is that it will include two influenza A viruses (H1N1 and H3N2) and one influenza B virus.
“There are some differences among the different influenza lineages. A/H3N2 is thought to be the most severe; A/H1N1 [is] somewhat less severe and may have a predilection for children. The B lineages usually do not produce large epidemics, often are more prominent later in the influenza season and may favor children,” explained William Schaffner, MD, a professor of preventive medicine, Department of Health Policy and Division of Infectious Diseases at Vanderbilt University Medical Center, in Nashville, Tenn.
Even though “flu is fickle,” and it can disobey the “rules,” Dr. Schaffner saw no risk to anyone getting quadrivalent vaccines, which include protection against B/Yamagata, that remain on the market while manufacturers adjust the formulation. “There may well be both trivalent and quadrivalent vaccines available this coming season (2024-2025). There are no advantages or disadvantages to receiving either type of influenza vaccine,” Dr. Schaffner explained.
The FDA and manufacturers have been working together to move from quadrivalent to trivalent seasonal influenza vaccines for the upcoming influenza season for as many Americans as possible.
Infectious Disease Special Edition spoke to one company that has been working closely with the FDA, CSL Seqirus, which will bring its complete portfolio of influenza vaccines to the U.S. market in trivalent formulations for the next influenza season.
“We have responded swiftly to meet the FDA’s directive and do not anticipate disruption to our manufacturing or on-time supply of doses to our U.S. customers,” said Gregg Sylvester, MD, the chief health officer at CSL Seqirus, in King of Prussia, Pa.
Dr. Sylvester explained that the composition of influenza vaccine formulations planned by CSL Seqirus for this upcoming season will be made to match the influenza strains that are expected to circulate this season. These strains were determined by the FDA through analysis of surveillance data related to the epidemiology and antigenic characteristics of recent influenza isolates, serologic responses to 2023-2024 vaccines, and the availability of candidate strains and reagents.
The removal of B/Yamagata also opens opportunities to improve public health and the vaccine supply, although these improvements so far are only theoretical. Researchers estimated that if there were a pivot to producing trivalent vaccines from quadrivalent vaccines, production of doses could increase by more than one-third. Furthermore, removal of B/Yamagata makes room for new strains of flu to possibly be included in future vaccines (Viruses 2022;14[8]:1745).
“While there has been some discussion on replacing the B/Yamagata strain with another influenza A strain, there has been no consensus or framework built around this, meaning at the moment no strain will take B/Yamagata’s place,” Dr. Sylvester noted.
Dr. Sylvester suggested that an influenza A strain is more likely to be a future addition to a new quadrivalent vaccine, saying, “Influenza A viruses are more common and change both genetically and antigenically, resulting in the ability to cause serious illness more easily. Influenza B viruses tend to evolve more slowly and have shorter, more predictable flu seasons.”
Dr. Schaffner reported no relevant financial disclosures. Dr. Sylvester reported no relevant financial disclosures other than his employment.
This article is from the April 2024 print issue.