A healthcare worker administers a dose of the Pfizer-BioNTech Covid-19 vaccine at a immunization clinic at the Peabody Institute Library in Peabody, Massachusetts, on Wednesday, January 26, 2022.
Vanessa Leroy | Bloomberg | Getty Images
The new omicron Covid boosters are unlikely to be very effective at preventing Covid infection and mild illness, 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 found in a real study published this week that the boosters are less than 50% effective compared to unvaccinated people for mild illness in almost all age groups.
In elderly, the booster dose given as the fourth dose was 19% effective in preventing mild disease compared to unvaccinated subjects. It was 23% effective against mild illness when given as the fifth dose.
Although the vaccine’s effectiveness against mild illness was low, those who received the booster did better than those who didn’t. The booster shot increased protection against minor disease by 28% to 56% compared to those who only received the old shots, depending on age and when the last dose was given.
The Food and Drug Administration approved the booster shots in late August with the goal of restoring the high level of protection that the vaccines had shown in late 2020 and early 2021. Back then, vaccines were more than 90% effective against infections. But the first real data from the CDC shows that the boosters are not meeting these high expectations.
“The boosters give you extra protection, but it’s not as strong, and you shouldn’t rely on it as your sole defense against infection,” said John Moore, professor of microbiology and immunology at Weill Cornell Medical College.
Moore said people at higher risk of Covid had every reason to get a booster as it slightly increases protection. However, he said common sense measures such as masking and avoiding large crowds remain important tools for vulnerable groups as the boosters are not very effective against infection.
The CDC study looked at more than 360,000 immune-healthy adults who were tested for Covid at retail pharmacies from September to November, when omicron BA.5 was dominant. Participants either received the booster shot, received two or more doses of the old shots, or were unvaccinated. It then compared those who tested positive for Covid to those who didn’t.
The study didn’t assess how well the booster shots worked against serious illnesses, so it’s still unclear whether they offer better protection against hospitalization than the old shots. The CDC said in a statement it will provide data on more severe episodes as it becomes available.
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Andrew Pekosz, a virologist at Johns Hopkins University, said the fact that the syringes offer some protection against infection in an era of highly immune-evasive omicron subvariants bodes well that they will offer strong protection against hospitalization . The vaccines have always performed better for serious illnesses than for minor illnesses, he said.
“It’s better than nothing. Certainly it doesn’t show that protection against infection is incredibly high,” Pekosz said. “I would expect then you would see even greater 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 wane over time.
“Protection against mild disease just isn’t as good in the era of the Omicron subvariants. The goal is protection against serious disease,” said Offit, an infectious disease expert at Children’s Hospital of Philadelphia who helped develop the rotavirus vaccine Has.
dr Celine Gounder, senior public health fellow at the Kaiser Family Foundation, said she was not troubled by the data. Reducing risk by even a modest amount at the individual level can have significant public health benefits at the population level.
“If you can reduce the risk by even 30%, even 20% in older people, that’s significant when 90% of COVID deaths are in that group,” Gounder said. “What matters to me is that you keep this 65-year-old out of the hospital.”
Dubbed bivalent vaccines, the boosters target both Omicron BA.5 and the original Covid strain, which first emerged in Wuhan, China in 2019. The original shots, dubbed monovalent vaccines, contain only the first strain of Covid.
It’s still unclear how the boosters will fare against more immune-evasive omicron subvariants like BQ.1 and BQ.1.1, which are now dominant in the US Pfizer and Moderna said last week that early clinical trial data show the boosters induce an immune response these subvariants.
According to CDC data, about 11% of those eligible for the new refresher, or 35 million people, have received it to date. About 30% of the seniors received the injection.