The World Health Organization advised on Friday Eliminating common ingredients in seasonal influenza vaccines It protects against certain virus strains. This is because that strain of the virus appears to no longer exist.
Influenza viruses of the B/Yamagata lineage have not been detected since March 2020, when the pandemic coronavirus SARS-CoV-2 was raging around the world. The explosive spread of the SARS-CoV-2 virus and associated health restrictions have dramatically disrupted the spread and cycles of other infectious diseases, including seasonal influenza.
The 2020-2021 influenza season was virtually non-existent, and the genetic diversity of circulating influenza strains collapsed dramatically. However, the B/Yamagata lineage seems to have been hit the hardest. Although other stocks have made a comeback in the years since, and the 2022-2023 season has already been intense in the U.S., the B/sea moth remains missing worldwide and appears to be extinct.
During a four-day meeting this week, WHO advisers met as usual to decide on the composition of the 2024 seasonal influenza vaccine for the Southern Hemisphere. Their recommendation, released today, does not contain ingredients that protect against B/Yamagata, making it the first time a health agency has recommended leaving a non-existent virus since B/Yamagata disappeared.
“The lack of confirmed detection of naturally occurring B/Yamagata lineage viruses indicates that the risk of infection by B/Yamagata lineage viruses is very low,” WHO advisors wrote in their final recommendation. “Therefore, the inclusion of the B/Yamagata lineage antigen in quadrivalent influenza vaccines is no longer justified and every effort should be made to exclude this component as soon as possible, the WHO Advisory Committee on Influenza Vaccine Composition said. This is the opinion of the association.”
Not only are viruses no longer a detectable threat, but as long as vaccines are being produced to fight them (a process that requires the virus to grow itself), leaving vaccine components around will prevent the virus from spreading. WHO advisers said there was a risk of reintroduction.
“While influenza vaccines are safe and effective, the production and use of inactivated or live-attenuated vaccines containing B/Yamagata lineage viruses poses a theoretical risk of reintroduction of B/Yamagata lineage viruses into the population. This risk can be reduced by eliminating the virus ‘B/Yamagata lineage virus from the vaccine,’ the advisors wrote.
B/Before Yamagata disappeared, there were four types of seasonal influenza circulating around the world, and seasonal influenza vaccination targets three or four of them (trivalent and quadrivalent vaccines, respectively). It was. The four virus types include two influenza A subtypes, H1N1 and H3N2, and two influenza B lineages, Victoria and Yamagata. (For a more detailed explanation of influenza, see this commentary.) Trivalent vaccines generally protect against both type A viruses and, in recent years, one type of B virus, the B/Victoria lineage. Masu.
The US uses quadrivalent shots. And since then, Northern Hemisphere 2023-2024 Influenza Vaccination Composition The decision was made several months ago and shots are now available for this season. They contain B/chevron components.