Early results from an experimental coronavirus vaccine show no major safety problems and suggest that it spurs the desired immune system responses, researchers reported today in the New England Journal of Medicine.

The U.S. government has awarded Novavax, a company based in Gaithersburg, Maryland, $1.6 billion to help develop and make the vaccine, which is given as two shots, three weeks apart. It includes a protein from the coronavirus to prompt the immune system to make antibodies to fight infection.

The study tested two dose levels in 108 healthy people and compared responses to 23 others who got placebo shots. Most of those given vaccine also received an adjuvant — a substance often included in vaccines to boost the immune system’s response and stretch a limited supply.

The adjuvant seemed safe; those who got it with the lower dose made antibodies in far greater numbers than what’s typically seen in people recovering from natural infection with COVID-19, researchers reported.

The work was sponsored by the Coalition for Epidemic Preparedness Innovations, a nonprofit focused on increasing vaccine availability worldwide.

Three other experimental vaccines are in late-stage testing in the United States.