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Omicron boosters are not very effective against mild illnesses

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A medical professional administers a dose of the Pfizer-BioNTech Covid-19 vaccine at a vaccination clinic at the Peabody Institute Library in Peabody, Massachusetts, U.S., Wednesday, January 26, 2022.

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The new omicron Covid boosters are unlikely to be very effective at preventing Covid infections and mild illnesses, but they will likely help keep the elderly and other vulnerable groups out of hospital this winter, experts say.

The Centers for Disease Control and Prevention, in a real-world study published this week, found that boosters are less than 50% effective against mild illness in nearly all adult age groups compared to unvaccinated people.

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

Although the effectiveness of the vaccine against mild illnesses was low, people who received the boosters were better off than those who did not. The booster boosted people’s protection against mild illnesses from 28% to 56% compared to those who had only received the older vaccines, depending on age and when they received their last dose.

The Food and Drug Administration authorized the recalls in late August in a bid to restore the high levels of protection the vaccines showed in late 2020 and early 2021. At that time, the shots were more than 90% effective against the infection . But the first real data from the CDC indicates that the boosters do not meet these high expectations.

“Boosters give you extra protection, but it’s not that strong, and you shouldn’t rely on it as your sole infection protection device,” said John Moore, professor of microbiology and immunology at Weill. Cornell Medical College.

Moore said those most at risk from Covid have every reason to get a booster as it slightly increases protection. But he said common sense measures such as masking and avoiding large crowds remain important tools for vulnerable groups, as reminders are not very effective against infection.

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

The study did not assess the performance of boosters against serious illnesses, so it is not yet clear whether they will provide better protection against hospitalization than older vaccines. The CDC, in a statement, said it would provide more severe outcome data when it becomes available.

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Andrew Pekosz, a virologist at Johns Hopkins University, said the fact that vaccines offer some protection against infection in an era of highly immune evasive omicron subvariants is a good sign that they will provide strong protection against hospitalization. Vaccines have always worked better against serious illnesses than mild ones, he said.

“It’s better than nothing. It certainly doesn’t show that the protection is incredibly high against infection,” Pekosz said. “I would expect you would see even greater protection against hospitalization or death then.”

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 wane over time.

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

Dr Celine Gounder, senior public health researcher 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 effect on public health at the population level.

“If you can reduce the risk in older people even by 30% or even 20%, that’s significant when 90% of COVID deaths are in that group,” Gounder said. “For me, what really matters is keeping this 65-year-old out of the hospital.”

The boosters, called bivalent vaccines, target both omicron BA.5 and the original Covid strain that first emerged in Wuhan, China in 2019. The original vaccines, called monovalent vaccines, only include the first Covid strain.

It remains unclear how the boosters will work against more immune evasive omicron subvariants, such as BQ.1 and BQ.1.1, which are now dominant in the United States. Pfizer and Moderna said last week that early clinical trial data shows the boosters induce an immune response against these subvariants.

About 11% of people eligible for the new booster, or 35 million people, have received it so far, according to CDC data. About 30% of seniors have received the vaccine.

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