U.S. regulators on Tuesday authorized another option for fall COVID-19 vaccination, updated shots made by Novavax.

Updated vaccines from Pfizer and Moderna began rolling out last month, intended for adults and children as young as 6 months. Now the Food and Drug Administration has added another choice, reformulated Novavax shots open to anyone age 12 and older.

The Centers for Disease Control and Prevention (CDC) already has urged most Americans to get a fall COVID-19 vaccination, shots tweaked to protect against a newer coronavirus strain. Novavax said shots will be available "in the coming days."

Protection against COVID-19, whether from vaccination or from an earlier infection, wanes over time. There's already been a late-summer increase in infections, and health officials hope enough people get the new shots to blunt a winter wave.

Novavax makes a protein-based vaccine mixed with an immune-boosting chemical, a different technology than the so-called mRNA vaccines made by Pfizer and Moderna.

While Pfizer and Moderna have shipped millions of doses, the fall rollout so far has been messy since, for the first time, the government isn't buying and distributing the COVID-19 shots. Ordering confusion from drugstores and doctors' offices, distribution delays and even bungled paperwork by insurance companies snarled early appointments.

The updated vaccine versions are supposed to be free through private insurance or Medicare, and the CDC has a program to temporarily provide free shots to the uninsured or underinsured.