A Phase 3, multicenter, randomized, double-blind, placebo-controlled, study (COV3001) of this vaccine was conducted in the United States, South Africa and South America to evaluate the efficacy, safety, and immunogenicity of a single dose of the vaccine. A total of 21,895 adults received COVID-19 Vaccine Janssen, and 21,888 adults received placebo. Individuals were followed for a median of 58 days. Efficacy against severe COVID-19 at 14 days was 76.7% and at 28 days 85.4%.
In the phase 3 clinical trial, Janssen COVID-19 vaccine was 76% efficacious against severe COVID-19.