Coronavirus Live Updates: Moderna and N.I.H. Begin Vaccine Trial

One of the first large studies of safety and effectiveness of a coronavirus vaccine in the United States began on Monday morning, according to the National Institutes of Health and the biotech company Moderna, which collaborated to develop the vaccine.

The study, a Phase 3 clinical trial, is to enroll 30,000 healthy people at about 89 sites around the country. Half will receive two shots of the vaccine, 28 days apart, and half will receive two shots of a saltwater placebo. Neither the volunteers nor the medical staff giving the injections will know who is getting the real vaccine.

The first shot was given to a person at 6:45 a.m., Dr. Anthony S. Fauci, the nation’s leading infections disease expert, said at a news briefing on Monday.

Dr. Fauci estimated that the full enrollment of 30,000 people in the trial would be completed by the end of the summer, and that results might be available by November. Even earlier results might be possible, he said, but added that he doubted that would be the case.

At the news briefing, Dr. Francis Collins, director of the National Institutes of Health, said that at least three more Phase 3 trials would be starting soon, each needing 30,000 patients. Those trials will involve vaccines made by Novavax, by a collaboration of the University of Oxford and AstraZeneca, and by Johnson & Johnson. All are part of the U.S. government’s Operation Warp Speed. A fourth vaccine, made by Pfizer and BioNTech, is also expected to start Phase 3 this month, but is not part of Warp Speed, Dr. Collins said.

Researchers will then monitor the subjects, looking for side effects and waiting to see if significantly fewer vaccinated people get Covid-19, indicating that the vaccine works. The main goal is to determine whether the vaccine can prevent the illness. The study will also try to find out if it can prevent severe Covid-19 and death; if it can prevent infection entirely, based on lab tests; and if just one shot can prevent the illness.

Earlier tests of the vaccine showed that it stimulated a strong immune response, with minor and transient side effects like sore arms, fatigue, achiness and fever. But exactly what type of immune response is needed to prevent the illness is not known, so Phase 3 studies are essential to determine whether a vaccine really works.