The Food and Drug Administration on Wednesday authorized updated versions of Pfizer-BioNTech’s and Moderna’s Covid booster shots that target the highly contagious BA.5 omicron subvariant.

The FDA authorized Pfizer’s modified booster for people ages 12 and older; Moderna’s shot was authorized for those 18 and up.

People who’ve received the two-dose primary series of either vaccine and those who’ve received the initial two doses plus one or two boosters are eligible for the updated shots as long as two months have passed since their last shot, the agency said in a statement.

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Image: Pfizer Covid-19 booster
A Pfizer COVID-19 vaccine booster shot is administered to a patient in Freeport, N.Y. on Nov. 30, 2021.Steve Pfost / Newsday via Getty Images file

“The public can be assured that a great deal of care has been taken by the FDA to ensure that these bivalent Covid-19 vaccines meet our rigorous safety, effectiveness and manufacturing quality standards for emergency use authorization,” Dr. Peter Marks, the agency’s top vaccine regulator, said in a statement.

The FDA’s signoff isn’t the last step: The decision will now go to the Centers for Disease Control and Prevention and its advisory committee to issue their own recommendation on how the shots should be used. The agency’s Advisory Committee on Immunization Practices is scheduled to vote Thursday. CDC Director Dr. Rochelle Walensky could sign off on the doses shortly after Thursday’s meeting, and vaccinations could begin widely after Labor Day.

The U.S. government agreed to purchase 105 million doses of Pfizer’s vaccine and 66 million doses of Moderna’s vaccine. 

Both modified boosters target the BA.4 and BA.5 omicron subvariants, in addition to the original coronavirus strain, in a single shot.

The FDA convened its outside advisory committee in June to review data on a different version of a booster — one that combined the original strain with an earlier version of omicron, called BA.1. At the time, the committee voted in favor of updating the shot to target omicron, but it did not specify which particular subvariant.

The FDA did not consult its advisory committee again before Wednesday’s authorizations.

The Biden administration is preparing to distribute the updated shots to teenagers and adults as part of its fall booster campaign. The hope, officials have said, is that modifying the vaccines to better match circulating strains will improve the shots’ effectiveness and perhaps provide longer-lasting immunity.

BA.5 makes up nearly 90% of all new Covid cases in the United States, according to the CDC.

Still, some outside scientists say the federal government may be rushing out the new vaccines too soon.

The modified boosters have been tested in animal studies, but studies in people have yet to be completed. The concern, some say, is that human studies may find that the new vaccines are no better than the existing shots, potentially decreasing public trust in the nation’s vaccine campaign.

“Where is the data that suggests it’s any better than giving just a boost with the ancestral strain?” said Dr. Paul Offit, a vaccine expert at the Children’s Hospital of Philadelphia and a member of the FDA’s vaccine advisory committee.

The government has already struggled to persuade Americans to get their first booster dose. Less than half of Americans who are eligible to get their first booster dose have received one, according to the CDC.

Still, other scientists say it “makes sense” to update the vaccines to match the dominant strains. The process is similar to the flu vaccine, when scientists, each year, select and test what strain or strains should be included in the shot.

“These vaccines will likely offer better, but not perfect, protection against infection with omicron and will provide better protection against symptomatic illness,” said Dr. Anna Durbin, a vaccine researcher at Johns Hopkins University in Baltimore.

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