Johnson & Johnson said on Friday that its single-dose vaccine was 66% effective in preventing Covid-19 in a large global trial against multiple variants, giving health officials another weapon to tackle the pandemic.

In the trial of nearly 44,000 volunteers, the level of protection against moderate and severe Covid-19 varied from 72% in the United States, to 66% in Latin America and just 57% in South Africa, from where a worrying variant has spread.