The Food and Drug Administration on Wednesday cleared Novavax shots for adults as the latest option for the U.S. in a COVID-19 vaccine.

Novavax, aleady available in Europe, makes a more traditional type of shot than the three other COVID-19 vaccines available in the U.S.

The FDA authorized Novavax’s initial two-dose series for people 18 and older.

“I encourage anyone who is eligible for, but has not yet received, a COVID-19 vaccine to consider doing so,” FDA Commissioner Dr. Robert Califf said in a statement.

According to The Associated Press, nearly a quarter of American adults still haven’t gotten their primary vaccinations.

The Maryland company also hopes its shots can become a top booster choice in the U.S. and beyond. Tens of millions of Americans still need boosters that experts call critical for the best possible protection as the coronavirus continues to mutate.

Before shots begin, the Centers for Disease Control and Prevention must recommend how they should be used, a decision expected next week.

Novavax CEO Stanley Erck told The Associated Press that he expected the U.S. to expand use of the vaccine beyond unvaccinated adults fairly quickly.

Already the FDA is evaluating it for those as young as 12, Erck said. Novavax also has submitted data on booster doses, including “mix-and-match” use in people who’d earlier received Pfizer or Moderna vaccinations.

The Biden administration has bought 3.2 million Novavax doses so far, and Erck said vaccinations should begin later this month.

The Associated Press contributed to this report.