This year’s flu shot will be missing a strain of influenza it’s protected against for more than a decade. That’s because there have been no confirmed flu cases caused by the Influenza B/Yamagata lineage since spring 2020. And the Food and Drug Administration decided this year that the strain now poses little to no threat to human health.
Scientists have concluded that widespread physical distancing and masking practiced during the early days of COVID-19 appear to have pushed B/Yamagata into oblivion . This surprised many who study influenza, as it would be the first documented instance of a virus going extinct due to changes in human behavior, said Dr. Rebecca Wurtz , an infectious disease physician and epidemiologist at the University of Minnesota School of Public Health.
“It is such an interesting and unique story,” Wurtz said, adding that if it were not for COVID, B/Yamagata would still be circulating. One reason COVID mitigation efforts were so effective at eliminating B/Yamagata is there was already a fair amount of immunity in the population against this strain of flu, which was also circulating at a lower level, said Dr. Kawsar Talaat , an infectious disease physician at Johns Hopkins Bloomberg School of Public Health.
In contrast, SARS-CoV-2 was a brand new virus that no one had encountered before; therefore, masking and isolation only slowed its transmission, but did not stop it. The absence of B/Yamagata won’t change the experience of getting this year�.