Flu shot a ‘major mismatch’ for dominant strain of influenza, but still offers protection

Even if it doesn't match the current mutated virus, researchers say the flu shot still offers protection from hospitalization and severe disease.

Dave Yasvinski 3 minute read December 21, 2021
Syringe with medical supplies

But while the vaccines may not be as effective at stopping infection as in previous years, they still prevent severe disease and death. GETTY

The current influenza vaccines are not a good match for the main strain of the virus, according to new research that suggests Canada could be in for its worst flu season in almost a decade.

The vaccines, which are prepared six months in advance, are designed to provide protection against strains of influenza that scientists believe will be most common in a given year, according to CNN. While this year’s version inoculates against H3N2, H1N1 and two strains of influenza B, it appears to be a poor match for a mutated version of H3N2 (known as 2a2) that is circulating widely in the U.S., according to a new report that is awaiting peer review.

“We have been monitoring this virus for several months,” said Scott Hensley, a professor of microbiology at the University of Pennsylvania who led the research. “From our lab-based studies, it looks like a major mismatch.”

But while the vaccines may not be as effective at stopping infection as in previous years, they still prevent severe disease and death, Hensley said, making the flu shot more important than ever.

“Studies have clearly shown that seasonal influenza vaccines consistently prevent hospitalizations and deaths even in years where there are large antigenic mismatches,” the report said. “Influenza vaccinations will be crucial for reducing hospitalizations as SARS-CoV-2 and 2a2 H3N2 viruses co-circulate in the coming months.”

The U.S. and Canada experienced a lighter than usual flu season last year as large portions of the planet stayed home, self-isolated and adhered to social distancing and other precautions in response to COVID-19. Now, health officials fear the two rapidly replicating viruses could combine to contribute to another cold, dark winter.

“Population immunity against influenza viruses is likely low since these viruses have not circulated widely during the COVID-19 pandemic,” the report said. “Social distancing, mask wearing, and decreases in international travel have likely contributed to reduced global circulation of influenza viruses. Once COVID-19-related restrictions are eased or lifted, it is possible that influenza viruses will circulate widely due to lack of infection-induced population immunity over the past two years.”

The mutations to the H3N2 strain of influenza are similar to those encountered during the 2014-15 flu season, Hensley said, a particularly bad period of time when vaccine effectiveness dipped to as low as six per cent, according to the U.S. Centers for Disease Control and Prevention. Vaccinations still made a big difference back then, the CDC said, estimating that inoculation prevented nearly 40,000 hospitalizations and 4,000 deaths in the U.S. that season.

“Influenza vaccination is the best protection against severe disease and illness,” Hensley said. “Even in these years of mismatch, we see high effectiveness against hospitalizations and severe disease.”

As the virus continues to evolve, it is possible that the protections provided by the vaccines will prove useful down the road. “While cases of 2a2 H3N2 infections are quickly rising in the United States and other parts of the world, it is possible that other clades of H3N2 will become predominant in the future,” the report said.

“It is also possible that H1N1 or influenza B viruses might dominate later in the 2021-2022 season.”

Dave Yasvinski is a writer with Healthing.ca

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