Johnson & Johnson's coronavirus vaccine proved safe and provoked an immune response in young and elderly volunteers alike, according to trial results published Wednesday in the New England Journal of Medicine. Most trial participants got just one shot of a high or low vaccine dose, or a placebo, although some people aged 18 to 55 got two doses. Most of the volunteers who got the vaccine produced the neutralizing antibodies, which defend cells from the virus, after 28 days. Researchers reported some side effects, including fever, fatigue, headache, and pain at the injection site. Dr. Paul Stoffels, chief scientific officer at J&J, said the data gave the company "confidence" the vaccine will prove highly effective. Results from the larger phase-three trial are expected later this month.