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The Food and Drug Administration is advising vaccine makers to reformulate their Covid-19 shots to target the BA.4 and BA.5 Omicron subvariants as well as the original strain of the virus, the agency announced Thursday, as it seeks to provide people with broader protection against the evolving coronavirus.

The BA.4 and BA.5 variants of Omicron — which have identical forms of the virus’s spike protein that the vaccines are designed to target — together now account for the majority of infections in the United States and have been building in prevalence globally.


The FDA had to provide its recommendation this summer so that vaccine makers have enough time to adapt their formulas and manufacture shots should a fall and winter booster campaign be necessary. The two-component shot is known as a bivalent vaccine.

“As we move into the fall and winter, it is critical that we have safe and effective vaccine boosters that can provide protection against circulating and emerging variants to prevent the most severe consequences of Covid-19,” Peter Marks, the FDA’s top vaccine regulator, said in a statement.

The FDA’s recommendation came after the agency held a meeting Tuesday with its outside vaccine experts, who voted overwhelmingly in favor of including an Omicron component in updated booster shots.


Researchers have found that the ongoing evolution of the SARS-CoV-2 virus has undercut the effectiveness of vaccines over time, particularly the protection the shots provided against infection. Protection against severe outcomes, such as hospitalization and death, has been broadly maintained even in the face of a changing virus, particularly with booster shots. The mutations included in the Omicron variants and fears about another potential fall and winter wave, however, have led scientists to call for updated vaccines.

The newer forms of the shots will only be offered as boosters, Marks said. The primary series of shots will continue to use the original vaccines, “since a primary series with the FDA-authorized and approved Covid-19 vaccines provides a base of protection against serious outcomes of Covid-19,” he said.

Vaccine makers have been developing a range of bivalent vaccines as different variants have emerged. Marks said that vaccine makers should submit the data they’ve generated on their bivalent shots that target the BA.1 form of Omicron to the FDA so that the agency can review them as it considers the authorization of bivalent booster shots.

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