There is a flu outbreak in the USA: why the vaccine against the virus was useless this year

The researchers reported on December 23 that one of the major circulating influenza viruses has changed and current influenza vaccines are no longer suitable for it. But they can still prevent severe illness, reports CNN

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“Based on our laboratory studies, this appears to be a serious discrepancy,” said Scott Hensley, a professor of microbiology at the University of Pennsylvania who led the study.

“This is bad news for the vaccine,” he said.

Influenza vaccines protect against four different strains of influenza: H3N2, H1N1, and two strains of influenza B.

Hensley's study only covers H3N2, but this is the main circulating strain.

Vaccine inadequacies may help explain a flu outbreak at the University of Michigan last month that affected more than 700 people. More than 26% of those who tested positive had been vaccinated against influenza, the same as those who tested negative. This indicates that the vaccine is not effective in preventing infection.

“That’s what influenza viruses do,” Hensley said. -We have been monitoring this virus for several months. Influenza viruses mutate constantly, much more frequently than other viruses, including the coronavirus. And different variations can circulate at the same time. But this version of H3N2 has changes that help prevent the body from producing antibodies in response to vaccines."

Antibodies are the first line of defense against invaders such as viruses, and the current vaccine does not appear to generate any proper antibodies against this new mutated version of H3N2, called 2a2 for short.

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Hensley said fortunately, the changes are unlikely to affect the second line of defense offered by the immune system - cells called T cells, so even if the vaccines don't protect against infection, they will likely protect people from severe illness and death.

“Studies have clearly shown that seasonal influenza vaccines consistently prevent hospitalizations and deaths, even in years with large antigenic mismatches,” Hensley and colleagues wrote in the report.

“Influenza vaccination will be critical in reducing hospital admissions as SARS-CoV-2 and 2a2 H3N2 viruses circulate simultaneously in the coming months,” he said.

The US Centers for Disease Control and Prevention said the flu all but disappeared last year but will return this year.

The big fear is the “double whammy” of influenza and Covid-19.

“Population immunity against influenza viruses is likely low because these viruses have not become widespread during the COVID-19 pandemic,” Hensley’s team wrote.

“Social distancing, wearing masks and reducing travel abroad have likely contributed to the reduction in the global spread of influenza viruses. With the easing or lifting of restrictions related to COVID-19, it is possible that influenza viruses will spread widely due to the lack of immunity in the population over the past two years, ”he said.

The effectiveness of influenza vaccines varies from year to year. Part of the problem lies in the time it takes to develop influenza vaccines. Most of them are produced using old technology, which requires the use of chicken eggs incubated for several weeks. Thus, influenza strains spread six months before vaccines are manufactured.

According to Hensley, the virus could evolve during this time, or different strains could become dominant, and it looks like it happened this year.

According to the CDC, over the years when a vaccine does not match the circulating viruses, vaccine effectiveness drops sharply—sometimes by as much as 6%.

The changes in the H3N2 virus this year are reminiscent of the mutations that made the vaccine so weak in 2014-2015, Hensley said.

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The researchers noted that things could still change.

“Although the number of 2a2 H3N2 infections is rapidly increasing in the United States and other parts of the world, it is possible that other H3N2 species will become dominant in the future. It is also possible that H1N1 or influenza B viruses may predominate later in the 2021-2022 season,” they wrote.

It is not clear to what extent the vaccines can match these strains. The flu kills between 12 and 000 people a year, depending on the flu season, and hospitalizes up to 52, according to the CDC.

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