The U.S. Food and Drug Administration (FDA) on Thursday approved updated COVID-19 vaccines made by Pfizer and Moderna targeting a recent variant of the disease, in time for a fall vaccination campaign.

The updated shots target the KP.2 variant that was circulating earlier this year. They are expected to be available across the country in the coming days, the companies said.

The health regulator had asked vaccine manufacturers in June to target the variant, if feasible.

The latest vaccines are designed to more closely target currently circulating variants and better protect against the disease's severe symptoms. The older shots targeted a variant that is no longer circulating.

"Vaccination continues to be the cornerstone of COVID-19 prevention," said Peter Marks, director of the FDA's Center for Biologics Evaluation and Research.

KP.2 is no longer dominant but is still related to other variants currently circulating in the United States. Health regulators hope to protect against circulating variants by targeting closely related forms such as KP.2.

The FDA cleared the use of Moderna's shot, branded as Spikevax, and Comirnaty, which is jointly developed by Pfizer and BioNTech, in both children aged six months and older, and adults.

The shots for children below 12 years are cleared under the agency's emergency use authorization pathway.

The regulator did not approve a more traditional protein-based shot made by Novavax, which can offer an alternative to people skeptical of the mRNA vaccines made by Moderna and Pfizer.

Novavax said it was working "productively" with the FDA and expects to have authorization in time for peak vaccination season.

The company told Reuters it has been manufacturing the updated shots in anticipation of authorization for months.

Novavax's vaccine is developed in moth cells and takes months to manufacture. In 2023, for instance, the company said it needed six months to bring an adequate supply of the vaccine to the market.

The approvals come at a time when COVID-19-related hospitalizations and deaths have increased over the past three months in the United States. Demand for the shots, however, has fallen sharply since the peak of the pandemic.