The Food and Drug Administration authorized Covid booster shots that target the omicron BA.5 subvariant as the U.S. prepares for another surge of infections this fall and winter.

It is the first time the FDA has authorized an updated vaccine formula since the original shots rolled out in Dec. 2020. Pharmacies are expected to start administering the new boosters after Labor Day weekend.

The U.S. has secured 171 million doses of Pfizer’s and Moderna’s updated shots so far, according to the Health and Human Services Department.

Pfizer’s new booster dose is authorized for people ages 12 and older, while Moderna’s new shots are authorized for adults ages 18 and older. The eligible age groups can receive the boosters two months after completing their primary series or their most recent booster with the old shots.

The Centers for Disease Control and Prevention has to sign off on the boosters before pharmacies can give them to patients. The CDC’s independent advisory committee is scheduled to meet on Thursday and Friday to review the data and issue its recommendations for health-care providers.