Federal officials approved a new COVID-19 vaccine made by Moderna late Friday but with limits on who can use it — not a replacement for the company’s existing shot, but a second option.

The new vaccine, mNexspike, is a step toward next-generation coronavirus vaccines. It’s made in a way that allows for a lower dose — a fifth of the dose of its current COVID-19 vaccine, Spikevax — by refining its immune target.

The approval “adds an important new tool to help protect people at high risk of severe disease from COVID-19,” Stephane Bancel, Moderna’s CEO, said in a statement Saturday.

Moderna is based in Cambridge.

The Food and Drug Administration approved the new vaccine for use in all adults 65 and older, and for people age 12 to 64 who have a least one health condition that puts them at increased risk from the coronavirus.

That’s the same limit that the FDA set in licensing another COVID-19 vaccine option from competitor Novavax.

Those restrictions are a departure from how the U.S. has handled COVID-19 vaccines until now, reflecting skepticism about vaccines from Health Secretary Robert F. Kennedy Jr. and other Trump officials.

Moderna’s existing vaccine doesn’t face those limits and has long been used for anyone ages 6 months and older. The company said it expected to offer both options this fall.

The FDA’s approval was based on a study of 11,400 people age 12 and older that compared the new low-dose vaccine with Moderna’s existing vaccine. It found the new vaccine was safe and was at least as effective — and more by some measures — than the original shot, the company said.

The news came just days after the Trump administration canceled funding for Moderna to develop a vaccine against potential pandemic flu viruses, including the H5N1 bird flu, despite promising early study results.