The New York Times, September 21, 2021
A second dose of Johnson & Johnson’s vaccine substantially increased its protection against Covid-19, the company announced Tuesday morning.
In a clinical trial, researchers found that two doses of the vaccine delivered 94 percent efficacy against mild to severe Covid-19 in the United States, up from 74 percent conferred with a single shot, the company reported. And two shots showed 100 percent efficacy against severe disease, although that estimate had a wide range of uncertainty.