WASHINGTON, Jan. 29 (Reuters) - Johnson & Johnson on Friday (Jan 29) said its single-dose vaccine was 72 per cent effective in preventing COVID-19 in the US.

A lower rate of 66 per cent efficacy was observed in a larger global trial conducted across three continents and against multiple strains of the virus.

In a trial involving nearly 44,000 volunteers, the level of protection against moderate and severe COVID-19 was 66 per cent in Latin America and just 57 per cent in South Africa, where a particularly worrying variant of the novel coronavirus is circulating.

Those results compare to the high bar set by two authorised vaccines from Pfizer-BioNTech and Moderna, which were around 95 per cent effective when given in two doses. Those trials, however, were conducted mainly in the US, before the broad spread of new variants now under the spotlight.

Johnson & Johnson’s main study goal was the prevention of moderate to severe COVID-19, and the vaccine was 85 per cent effective in stopping severe disease and preventing hospitalisation across all geographies and against multiple variants 28 days after immunisation.

That level of prevention "will potentially protect hundreds of millions of people from serious and fatal outcomes of COVID-19," Dr Paul Stoffels, Johnson & Johnson’s chief scientific officer, said in a statement.