A prototype vaccine has protected monkeys from the coronavirus, researchers reported Wednesday, a finding that offers new hope for effective human vaccines.

Scientists are already testing coronavirus vaccines in people, but the initial trials are designed to determine safety, not how well a vaccine works. The research published Wednesday offers insight into what a vaccine must do to be effective and how to measure that.

“To me, this is convincing that a vaccine is possible,” said Dr. Nelson Michael, director of the Center for Infectious Diseases Research at Walter Reed Army Institute of Research.

Scientists are engaged in a worldwide scramble to create a vaccine against the new coronavirus. Over a hundred research projects have been launched. Early safety trials in humans have been started or completed in nine of them.

Next to come are larger trials to determine whether these candidate vaccines are not just safe, but effective. But those results won’t arrive for months.

In the meantime, Dr. Dan Barouch, a virologist at Beth Israel Deaconess Medical Center in Boston, and his colleagues have started a series of experiments to get a broader look at how coronaviruses affect monkeys — and whether vaccines might fight the pathogens. Their report was published in Science.

Barouch is working in a partnership with Johnson & Johnson, which is developing a coronavirus vaccine that uses a specially modified virus, called Ad26, that he developed.

The new research in monkeys “lays the scientific foundations” for those efforts, Barouch said. In March, the federal government awarded $450 million to Janssen Pharmaceuticals, a division of Johnson & Johnson, to develop a coronavirus vaccine.

The scientists started by studying whether the monkeys become immune to the virus after getting sick. The team infected nine unvaccinated rhesus macaques with the new coronavirus.

The monkeys developed symptoms that resembled a moderate case of COVID-19, including inflammation in their lungs that led to pneumonia. The monkeys recovered after a few days, and Barouch and his colleagues found that the animals had begun making antibodies to the coronavirus.

Some of them turned out to be so-called neutralizing antibodies, meaning that they stopped the virus from entering cells and reproducing.

Thirty-five days after inoculating the monkeys, the researchers carried out a “re-challenge,” spraying a second dose of the coronavirus into the noses of the animals. The monkeys produced a surge of protective neutralizing antibodies. The coronavirus briefly managed to establish a small infection in the monkeys’ noses but was soon wiped out.

These results don’t necessarily mean that humans also develop strong, long-lasting immunity to the coronavirus. Still, Barouch and others found the research encouraging.

“If we did the re-challenge study and it didn’t work, the implication would be that the entire vaccine effort would fail,” he said. “That would have been really, really bad news for 7 billion people.”

Florian Krammer, a virologist at the Icahn School of Medicine at Mount Sinai in New York who was not involved in the study, said that the levels of antibodies seen in the monkeys were promising.

“This is something that would protect you from disease,” he said. “It’s not perfect, but you certainly see protection.”