The Food and Drug Administration authorized the Novavax COVID-19 vaccine for people 18 and older, the fourth shot cleared in the United States.

It’s a different type of vaccine than the ones already on the market in the US — it’s a protein-based vaccine that delivers pieces of the virus spike protein directly to the body.

Clinical trials found that the shot was 90 percent effective at preventing COVID-19. The trials, though, were conducted in early 2021 — before the delta and then omicron variants of the virus took over, so those numbers would likely be lower now.