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.

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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.

Image: Pfizer Covid-19 booster (Steve Pfost / Newsday via Getty Images file)
Image: Pfizer Covid-19 booster (Steve Pfost / Newsday via Getty Images file)© Provided by NBC News

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.

Dr. Peter Marks, the FDA’s top vaccine regulator, said on a call with reporters on Wednesday that health officials expect the updated boosters will provide increased protection against the BA.5 omicron subvariant.

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

"A great deal of care has been taken by the FDA to ensure that these updated boosters meet our rigorous safety, effective and manufacturing quality standards for emergency use authorization," he said on the call.

The agency's two-month gap recommendation for receiving the updated shots is meant in part to ensure that there’s enough time for the shots to build a good immune response, Marks said.

He also said that gap should reduce the risk of a rare heart inflammation condition called myocarditis. Both Pfizer's and Moderna's first iteration of the Covid vaccines have been linked to a small but increased risk of the heart condition, particularly in young men. Marks said a wider gap between doses appears to reduce the risk of the condition.

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.

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.

Marks said Wednesday that the agency expects data on how well the new boosters perform in humans in "one to two months."

He said process for updating Covid boosters is similar to the process used for the flu vaccine, when scientists, each year, select and test what strain or strains should be included in the shot. The FDA does not require clinical trials in humans before making changes to the flu vaccine.

The FDA's policy for flu shots comes after decades of experience with making updates to those vaccines, but Marks said the agency is "comfortable" taking the same approach with the Covid boosters.

"We understand how the vaccine works really well," he said.

Other scientists say it “makes sense” to update the vaccines to match the dominant strains.

“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.

The FDA commissioner, Dr. Robert Califf, on the call urged the public to get whatever Covid booster that is available to them when eligible, noting the original Covid boosters — which are still a part of the updated version — are highly effective in preventing severe illness. As of now, people under age 12 are ineligible to receive the updated booster doses, but can still get a regular booster.

The added BA.5 component is "just icing on the cake," he said.

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