Johnson & Johnson said Wednesday it started a 60,000-person clinical trial of its single-dose Covid-19 vaccine on three continents, becoming the fourth experimental Covid-19 jab to enter final-stage testing in the US.

The New Brunswick, New Jersey company said it could learn pivotal results from the trial by early next year, which if positive could lead to government authorization of the vaccine for emergency use soon afterward. J&J aims to enroll adult volunteers in the US and several other countries, including Brazil and South Africa.