Flu Vaccine 'A Major Mismatch' For 2021's Dominant Strain: Report

ACROSS AMERICA — The flu vaccine received by millions of Americans this winter may be a bad match for this year's dominant influenza strain, according to reports.

This season's dominant flu strain is H3N2, a type of influenza A virus, according to the Centers for Disease Control and Prevention. While the flu vaccine typically protects against four strains of the flu — H3N2, H1N1 and two strains of influenza B — an ongoing study on H3N2 suggests it may be mutating in a way that causes it to evade vaccine-created antibodies meant to defend against the virus.

"From our lab-based studies it looks like a major mismatch," Scott Hensley, a professor of microbiology at the University of Pennsylvania who led the study, told CNN. While that's bad news for the vaccine, "that's what viruses do," Hensley said.

Hensley and his team have been monitoring the H3N2 strain for any genetic mutations that occur when the virus spreads. Through their surveillance, they identified the mutation that helps H3N2 evade vaccine antibodies, LiveScience reported.

The group's study has not yet been peer-reviewed or published in a scientific journal, and it only measured antibody responses in 40 individuals who were mostly young and healthy, according to LiveScience.

The group's finding doesn't mean the flu vaccine is worthless. It should still prevent serious illness.

"Studies have clearly shown that seasonal influenza vaccines consistently prevent hospitalizations and deaths even in years where there are large antigenic mismatches," the authors wrote. "So even if this year's flu shot doesn't match the dominant strain, the vaccines will reduce the odds of severe disease and death."

So far this season, the CDC has recorded 7,516 cases of the flu, a 1.3 percent positivity rate.