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For 10 years, Americans have had access to flu vaccines that protect against four strains of the virus: two A strains and two B strains.
However, starting this fall, all flu vaccines distributed in the United States will likely contain only three strains, and the change is due to Covid-19.
In 2020, all the precautions that helped people avoid Covid had an unexpected benefit: an entire branch of the flu family tree, a B strain that geneticists call the Yamagata clade, disappeared and has not been detected since. .
A strain of Yamagata was typically included in each year’s flu vaccine recipe, so vaccine designers were faced with a dilemma: should they remove the strain from the formula or keep it, since it is known that B viruses are sneaky?
In the 1990s, when Yamagata was at its peak, another branch of the B strain flu virus, called Victoria, was seen only sporadically in testing, but had a resurgence in the 2000s. What if Yamagata Will he return after a long absence? It is not quick or easy to change the way flu vaccines are made, and those changes require regulatory review and approval.
In September, the World Health Organization said that “inclusion of Yamagata lineage antigens in influenza vaccines is no longer justified,” and in October, vaccine experts advising the U.S. Food and Drug Administration The US also said that the Yamagata strains should be eliminated as soon as possible. as possible.
“We’ve been talking about this for four years,” said Dr.
Paul Offit, director of the Vaccine Education Center at the Children’s Hospital of Philadelphia and member of the FDA’s Vaccines and Biologics Advisory Committee (VRBPAC).
The committee will meet Tuesday to discuss next steps and vote on flu vaccine recommendations for the fall.
Offit said he expects all flu vaccines available in the U.S. this fall to be three-strain, or trivalent, vaccines, with two A strains and a B/Victoria strain, but no B/Yamagata strain, according to recommendations of the WHO and VRBPAC.
There are good reasons to abandon the Yamagata strain, Offit said.
“You don’t want to vaccinate people for something they don’t need,” he said.
There may also be some harm in continuing to include it, said Dr. Jodie Guest, senior vice chair of the Department of Epidemiology at Emory University’s Rollins School of Public Health.
“Every time these flu vaccines are produced, depending on which vaccines you’re talking about, live or attenuated viruses are used, and they have to be cultured,” he said. Growing something in a lab also means that it could escape from that lab.
“So while it would be an incredibly small anticipated risk, there is a chance to reintroduce it into the population by including it in a vaccine,” Guest said.
Other researchers have pointed that eliminating the Yamagata strain would free up production capacity to increase the number of doses manufactured globally, something that would benefit countries affected by the shortage.
in a article about the expected changes Published February 28 in the New England Journal of Medicine, Dr. Arnold Monto, one of the FDA’s vaccine advisors, Dr. Maria Zambon of the U.K. Health Security Agency, and Dr. Jerry Weir of The FDA said the move opens the door to considering a new vaccine. formulas.
Because the B/Victoria and A/H1N1 strains of the vaccine are typically more effective than the A/H3N2 component, some experts have suggested doubling the H3N2 dose or perhaps introducing a second member of that family.
But as the authors point out, any such change would require testing and regulatory approval, and for that reason, we’re not likely to see the return of four-strain flu vaccines anytime soon. Instead, they say, it will be “more of a long-term goal to improve the effectiveness of the vaccine.”