Omicron boosters are not very effective against minor illnesses

A healthcare worker administers a dose of Pfizer-BioNTech Covid-19 vaccine at the vaccination clinic at the Peabody Institute Library in Peabody, Massachusetts, USA on Wednesday, January 26, 2022.

Vanessa Leroy | Bloomberg | Getty Images

Experts say the new Covid omicron boosters are probably not very effective at preventing Covid infections and minor illnesses, but they will likely help keep the elderly and other vulnerable populations out of hospital this winter.

Centers for Disease Control and Prevention, Mr. real study published this weekfound that boosters were less than 50% effective against mild illness in nearly all age groups compared to unvaccinated people.

For the elderly, booster was 19% more effective in preventing minor illness when given as the fourth dose compared to unvaccinated people. It was 23% effective against mild illness when taken as the fifth dose.

Although the effectiveness of the vaccine against mild diseases was low, people who received a booster felt better than those who did not receive it. Revaccination increased people’s protection against mild illness by 28-56% compared to those who received only the old shots, depending on age and the time they received their last dose.

The FDA authorized boosters at the end of August to restore the high level of protection demonstrated by vaccines in late 2020 and early 2021. At the time, vaccinations were more than 90% effective against infection. But the first real data from the CDC shows that the boosters fall short of those lofty expectations.

“Boosters give you some extra protection, but they’re not that strong and you shouldn’t rely on them as your only defense against infection,” said John Moore, professor of microbiology and immunology at Weill Cornell Medical College.

Moore said there is good reason for people at higher risk of contracting Covid to get a booster as it boosts protection slightly. But he said common-sense measures, such as masking and avoiding large crowds, remain important tools for vulnerable groups as boosters are not very effective against infection.

The CDC study included more than 360,000 adults with healthy immune systems who were tested for Covid at retail pharmacies from September to November, when omicron BA.5 was dominant. Participants either received a booster, two or more doses of older shots, or were not vaccinated. He then compared those who tested positive for Covid with those who did not.

The study did not evaluate how well boosters work against severe illness, so it is still unclear if they will provide better protection against hospitalization than older shots. The CDC said in a statement that they will provide data on more severe effects when they become available.

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Andrew Pekosh, a virologist at Johns Hopkins University, said the fact that vaccines offer some protection against infection in an era of high-immunity omicron subvariants is a good sign that they will provide strong protection against hospitalization. According to him, vaccines have always worked better against severe diseases than against mild ones.

“It’s better than nothing. Of course, this does not prove that protection against infection is incredibly high, ”Pekos said. “I expect you will then see even more protection from hospitalization or death.”

Dr. Paul Offit, a member of the FDA’s vaccine advisory committee, said trying to prevent mild illness is not a viable public health strategy because the antibodies that block infection simply weaken over time.

“Protection against mild disease isn’t all that great in the era of omicron subvariants. The goal is to protect against severe disease,” said Offit, an infectious disease expert at the Children’s Hospital of Philadelphia who helped develop the rotavirus vaccine.

Dr. Celine Gunder, senior fellow at the Kaiser Family Foundation, said she was not alarmed by the data. Reducing risk by even a modest amount at the individual level can have a significant positive impact on public health at the population level.

“If you can reduce the risk among older people by even 30%, even 20%, that’s important when 90% of COVID deaths are in this group,” Gonder said. “It really matters to me if you keep this 65-year-old from being hospitalized.”

The boosters, called bivalent vaccines, target both omicron BA.5 and the original strain of Covid, which first appeared in Wuhan, China in 2019. Initial shots, called monovalent vaccines, include only the first strain of Covid.

It is still unclear how the boosters will work against the more immune-evading omicron sub-variants such as BQ.1 and BQ.1.1 that currently dominate the US. Pfizer and Moderna said last week that data from early clinical trials show boosters elicit an immune response to these sub-options.

About 11% of those who qualify for the new booster, or 35 million people, have already received one, according to the CDC. About 30% of older people have been vaccinated.

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