New data from Britain suggests that booster protection against symptomatic Covid caused by the Omicron variant diminishes within 10 weeks.
There haven’t been enough severe cases of Omicron to calculate how well boosters protect against serious illness, but experts believe the injections will continue to provide significant protection against hospitalization and death.
“It will be a few weeks before its effectiveness against serious diseases with Omicron can be estimated,” according to the new report from the UK’s Health Security Agency. “However, based on experience with previous variants, this is likely significantly higher than the estimates against symptomatic disease.”
In the weeks since Omicron was discovered, multiple studies have suggested that the variant is adept at evading the antibodies produced after vaccination or after infection with the coronavirus.
The new report from Britain, which included data on people who had received the AstraZeneca, Pfizer or Moderna injections, confirmed that the vaccines — both the first two-shot series and booster doses — were less effective and declined more quickly. against Omicron than against Delta.
Of the people who received two doses of the AstraZeneca vaccine, a booster with one of the mRNA vaccines, made by Pfizer and Moderna, was 60 percent effective at preventing symptomatic disease two to four weeks after the injection. However, after 10 weeks, the Pfizer booster was only 35 percent effective. The Moderna booster was 45 percent effective for up to nine weeks. (The AstraZeneca vaccine is not authorized in the United States, but the Johnson & Johnson injection uses a similar technology.)
For people who received three doses of Pfizer, the vaccine’s effectiveness dropped from 70 percent one week after the booster to 45 percent after 10 weeks. In contrast, Pfizer recipients who received a Moderna booster seemed to do better; their vaccine regimen remained up to 75 percent effective for up to nine weeks.
The report, which was based on an analysis of approximately 148,000 Delta cases and 68,000 Omicron cases, also included recent data suggesting that Omicron infections are less likely to lead to hospitalizations than Delta infections. The findings should be interpreted with caution, the agency noted, as there have still not been many Omicron cases relatively, and the people who contracted the variant may not be representative of the wider population.
The Biden administration has encouraged all eligible Americans to receive booster shots as Omicron proliferates.
In a recent interview on WCBS-AM, a radio station in New York, Dr. Anthony S. Fauci, the nation’s leading infectious disease physician, said officials were monitoring the effectiveness of mRNA boosters against Omicron.
“I think it’s premature, at least on the part of the United States, to talk about a fourth dose,” he said. Israel is considering giving its citizens a fourth chance.
Some scientists have warned against a fourth injection, noting that there is no evidence yet that it is needed and that some immune cells eventually stop responding to the injections if too many doses are given.