U.S. drug regulators on Wednesday approved two updated formulations of COVID-19 vaccines as booster shots intended to provide increased protection against the currently circulating Omicron variant.

The newly authorized single-dose shots will be for use at least two months after administration of the existing primary or booster vaccine. The updated booster from Pfizer Inc. will be available for those 12 years of age and older, while the new shot from Moderna Inc. is authorized for those at least 18 years old.

The so-called bivalent vaccines are meant to work against both the original strain of the novel coronavirus as well as the BA.4 and BA.5 Omicron subvariants, which have been prevalent in the United States.

"As we head into fall and begin to spend more time indoors, we strongly encourage anyone who is eligible to consider receiving a booster dose with a bivalent COVID-19 vaccine to provide better protection against currently circulating variants," U.S. Food and Drug Administration Commissioner Robert Califf said in a statement.

The FDA gave the greenlight based on safety data from the original vaccine and a bivalent vaccine targeting the BA.1 Omicron subvariant. Side effects are expected to be similar to those reported by individuals who have received existing vaccines, the FDA said.

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