Among all participants from different geographies, and those infected with an emerging viral variant, the vaccine was 66% effective overall in preventing moderate to severe COVID-19 at 28 days after vaccination. Researchers found the vaccine protected against moderate to severe COVID-19 infection by 72% in the U.S., 66% in Latin America, and 57% in South Africa 28 days after vaccination. However, some protection was observed as early as day 14.

In terms of severe COVID-19, the vaccine was 85% effective across all regions studied 28 days after vaccination. In addition, efficacy increased over time with no cases in vaccinated participants reported after day 49, Johnson & Johnson said.

Regarding hospitalization and death, the vaccine candidate demonstrated complete protection 28 days after vaccination. Regarding medical intervention -- hospitalization, intensive care unit admission, mechanical ventilation, and extracorporeal membrane oxygenation (ECMO) -- Johnson & Johnson found no reported cases among participants who received the vaccine, 28 days after injection.

Trial participants will be followed for up to two years to assess safety and efficacy. The comprehensive dataset will be submitted to a peer-reviewed journal in the coming weeks, the firm said.