American pharmaceutical firm Johnson & Johnson announced Friday its vaccine candidate has a 66% overall effectiveness in preventing moderate to severe COVID-19, 28 days after vaccination.

Its Phase 3 clinical trials were based on 43,783 participants accruing 468 symptomatic cases of COVID-19, but the vaccine's effectiveness varied widely in different regions.

The level of the vaccine's protection was 72% in the US, 66% in Latin America and 57% in South Africa, according to the company.

The vaccine has 85% effectiveness in preventing severe disease caused by COVID-19, and it demonstrated complete protection against COVID-19 related hospitalization and death as of Day-28.

Johnson & Johnson said it plans to apply for emergency use authorization in the US early February and expects to have product available to ship immediately following authorization.

On Thursday, another US pharmaceutical firm Novavax announced its vaccine has over 89% effectiveness in preventing people from contracting COVID-19.

A separate trial by the firm, however, found out that it has an efficacy of only 49.4% when about 92% of participants with COVID-19 had the variant seen in South Africa.