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Omicron boosters are not very effective against mild disease

A health worker gives a dose of the Pfizer-Biontech COVID-19 vaccine at an immunization clinic at the Peabody Institute Library in Peabody, Massachusetts, US, Wednesday, Jan. 26, 2022.

Vanessa Leroy | Bloomberg | Getty Images

Experts say the new Omicron Covid boosters may not be very effective at preventing Covid infection and mild illness, but they will help keep the elderly and other vulnerable groups out of hospital this winter.

Centers for Disease Control and Prevention, in A real-world study published this weekfound that boosters are less than 50% effective against mild disease in nearly all adult age groups compared to those who have not been vaccinated.

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

Although the effectiveness of the vaccine against mild disease was low, those who did not receive a booster fared better. Boosters increased people’s protection against mild disease by 28% to 56% compared to those who received their last dose, depending on age and age.

The Food and Drug Administration authorized the booster in late August with the goal of restoring the high level of safety of the vaccines demonstrated in late 2020 and early 2021. At the time, the shots were more than 90% effective against infection. But the first real-world data from the CDC indicates that boosters are not meeting those high expectations.

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

Moore said people at high risk from COVID have every reason to get a booster because it modestly increases protection. But he said common-sense measures such as wearing masks and avoiding large crowds are important tools for vulnerable groups because boosters have not been highly effective against infection.

The CDC study looked at more than 360,000 adults with healthy immune systems who got tested for COVID at retail pharmacies from September to November, when Omicron BA.5 was effective. Participants either received a booster, two or more doses of the old shots, or were not vaccinated. It then compared those who tested positive for Covid with those who did not.

The study didn’t evaluate how well the boosters fared against severe disease, so it’s still unclear whether they would provide better protection against hospitalization than the older shots. The CDC said in a statement that it would provide data on more serious outcomes when they become available.

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Andrew Pekoz, a virologist at Johns Hopkins University, said the fact that the shots are providing some protection against infection in the era of highly immunosuppressive evasive omicron subvariants is a good sign that they provide strong protection against hospitalization. will do. He said vaccines have always performed better against severe disease than mild disease.

Pekoz said, “It’s better than nothing. Certainly, it doesn’t kind of show that the protection against infection is incredibly high.” “I expect you’ll then see even greater protection from hospitalization or even death.”

Dr. Paul Offitt, a member of the FDA’s Vaccine Advisory Committee, said trying to prevent mild disease is not a viable public health strategy because antibodies that block infection wane over time.

“Protection against minor disease is not that great in the Omicron subvariant era. The goal is to avoid severe disease,” said Offit, an infectious disease specialist at the Children’s Hospital of Philadelphia who helped develop the rotavirus vaccine.

Dr. Celine Gounder, a senior public health fellow at the Kaiser Family Foundation, said she is not concerned by the data. Reducing exposure even by small amounts at the individual level can have a significant positive impact on public health at the population level.

“If you can reduce the risk among the elderly by 30%, even 20%, that’s significant when 90% of COVID deaths are occurring in that group,” Gounder said. “To me, what really matters is whether you’re keeping that 65-year-old man out of the hospital.”

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

It is still unclear how the boosters will perform against the more immune evasive Omicron subvariants, such as BQ.1 and BQ.1.1, which are now effective in the US Pfizer and Moderna last week said preliminary clinical trial data shows that the boosters induce an immune response against it. This subvariant.

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

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