The first COVID-19 vaccine tested in the United States revved up people's immune systems just the way scientists had hoped, researchers reported - as the shots are poised to begin key final testing.
"No matter how you slice this, this is good news," Dr Anthony Fauci, the US government's top infectious disease expert, told The Associated Press news agency.
The experimental vaccine, developed by Fauci's colleagues at the National Institutes of Health in partnership with Moderna Inc, will start its most important step around July 27: a 30,000-person study to prove if the shots really are strong enough to protect against the coronavirus.
But Tuesday, researchers reported anxiously awaited findings from the first 45 volunteers who rolled up their sleeves back in March. Sure enough, the vaccine provided a hoped-for immune boost.
Those early volunteers developed what are called neutralising antibodies in their bloodstream - molecules key to blocking infection - at levels comparable to those found in people who survived COVID-19, the research team reported in the New England Journal of Medicine.