Johnson & Johnson said that its single-dose vaccine was 66% effective in preventing Covid-19 in a large trial against multiple variants across three continents.
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.
A high bar has been set by two authorised vaccines from Pfizer/BioNTech and Moderna, which were around 95% effective in preventing symptomatic illness in pivotal trials when given in two doses.
Those trials, however, were conducted mainly in the United States and before new variants emerged. J&J's main goal was the prevention of moderate to severe