In one study, 56 volunteers produced a high level of antibodies against the virus without any dangerous side effects. In the other, researchers found that the vaccine strongly protected monkeys from coronavirus infections.

Although it’s not possible to directly compare the data from clinical trials of different coronavirus vaccines, John Moore, a virologist at Weill Cornell Medicine who was not involved in the studies, said the Novavax results were the most impressive he had seen so far.

“This is the first one I’m looking at and saying, ‘Yeah, I’d take that,’” Dr. Moore said.

Angela Rasmussen, a virologist at Columbia University who was not involved in the studies, called them “encouraging preliminary results,” but cautioned that it won’t be possible to say whether the vaccine is safe and effective until Novavax conducts a large-scale study — known as Phase 3 — comparing people who get vaccinated to people who get a placebo.