He noted that B/Yamagata tends to surge in certain years and then virtually disappear in others.
“Just the evidence we haven’t seen it for a while, I don’t think that by itself is a convincing argument,” Kennedy said. “Data suggesting that since we haven’t seen a single case since March 2020, that’s good, but I’d like to see a longer period where we don’t see any of it, because it’s hidden from us before, these lineages.”
Now, COVID restrictions have relaxed and kids are back in school, raising concerns among public health officials that this flu season could be a tough one. B/Yamagata could resurface, he said.
“These viruses are very good at making up for lost time and lost distance in this race,” Kennedy said. “We might get ahead, but if we don’t continue, we can’t get a handle on it.”
If B/Yamagata is truly gone for good, that means we could juggle the strains included in the annual flu vaccine to get more bang for our buck, said Dr. William Schaffner, medical director of the Bethesda, Md.-based National Foundation for Infectious Diseases.
The structure of the current flu vaccine includes four strains: influenza A/H3N2 (Hong Kong), influenza A/H1N1 (Swine), influenza B/Victoria, and influenza B/Yamagata. The influenza A strains tend to be more infectious and the source of deadly epidemics, while influenza B percolates more slowly among school-age children and teens.
Each year U.S. scientists play a guessing game to determine which genetic version of each of the four strains is likely to be the most infectious, Kennedy said. When they guess right, the flu vaccine provides better protection.
Replacing the B/Yamagata part of the vaccine with another strain that’s more infectious and dangerous could improve the shot’s effectiveness, Schaffner said.
“Could you double up on the next most severe strain, H3N2? Could you get two H3N2s in there?” Schaffner said.
Kennedy agreed. “Being able to pick another strain that’s not B, that’s an A strain, would probably help with that guessing game,” he said.