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New Covid boosters work better against infection than previous shots, CDC finds

The omicron booster shots performed better in preventing infections in all adult age groups, with more protection for people who waited longer to get them.
Vocational Nurse Cleopatra Oniya administers the Pfizer booster shot in Los Angeles on May 5, 2022.
Cleopatra Oniya, a nurse, administers the Pfizer booster shot in Los Angeles on May 5.Frederic J. Brown / AFP via Getty Images

The first real-world data on the new omicron vaccines find that they are better at preventing symptomatic Covid infections than the earlier doses, the Centers for Disease Control and Prevention said Tuesday.

The findings fortify messaging from public health officials that the new shots, from Pfizer-BioNTech and Moderna, should provide people with the best protection against Covid this winter, according to the CDC report.

Both Pfizer’s and Moderna’s new boosters target BA.4 and BA.5, along with the original coronavirus strain, in a single dose.

The vaccine efficacy from the new boosters isn't "stellar," said Dr. Ofer Levy, the director of the Precision Vaccines Program at Boston Children’s Hospital, noting that scientists would love to see a vaccine that blocks infections entirely.

But, he said, it is "something" and outperforms earlier doses of the original formulation.

The CDC’s results are based on more than 360,000 symptomatic adults tested for Covid at pharmacies nationwide from Sept. 14 to Nov. 11, when omicron subvariants BA.4 and BA.5 were the dominant strains in the United States.

People who got the updated booster shots after two or more shots of the original vaccine were compared to another group of people who received only two or more doses of the original vaccine. (The first iterations of Pfizer’s and Moderna’s vaccine target only the original coronavirus strain identified in late 2019.)

When should you get the Covid booster?

The updated booster shots performed better in preventing infections in all adult age groups, with higher vaccine efficacy seen in people who waited longer before getting the updated booster, the CDC found.

“That makes sense,” said John Moore, a professor of microbiology and immunology at Weill Cornell Medical College. He noted that studies have shown longer intervals between Covid vaccine doses can lead to higher antibody levels.

The CDC currently recommends that people 5 and older get an updated booster at least 2 months after their last dose. People who've recently had Covid should wait until they have recovered from the illness and ended isolation. But people may also consider delaying boosters for three months after infection, depending on risk factors.

The CDC study confirms earlier data from Pfizer and Moderna that suggested the updated vaccines are better than the old formula. But because those data only showed immune responses seen in blood samples, scientists were unable to determine how the new shots actually performed in the real world. 

Scientists have been eagerly awaiting real-world data. Both Pfizer’s and Moderna’s updated boosters were authorized by the Food and Drug Administration in late August without data from human trials — a move considered risky by some, especially if the new shots later proved to be no better than the existing vaccines. 

The CDC said its study has several limitations, including that vaccination status and medical history were self-reported and may be subject to bias. Previous Covid infections may be underreported, the agency said, and low uptake of the updated boosters could have affected the results.

Dr. Céline Gounder, a senior fellow at KFF, formerly known as Kaiser Family Foundation, and an infectious disease specialist, also noted that the CDC report looked at infections during the spread of omicron subvariants BA.4 and BA.5.

New subvariants BQ.1.1 and BQ.1 are on the rise in the U.S., she said, and it’s unclear how the updated boosters will perform against those strains.

Levy agreed, saying matching the vaccines to the currently circulating strains is like “playing whack-a-mole.”

Still, he urged people to get vaccinated, saying the updated booster shots should provide a good level of protection against the new variants.

“We’re not out of the woods,” he said.

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