Johnson & Johnson has launched a new large-scale late-stage trial to test a two-dose regimen of its experimental Covid-19 vaccine and evaluate potential incremental benefits for the duration of protection with a second dose.

The UK arm of the study is aiming to recruit 6,000 participants and the rest will join from other countries with a high incidence of Covid-19 cases such as the United States, Belgium, Colombia, France, Germany, the Philippines, South Africa and Spain, it said.

They will be given a first dose of either a placebo or the experimental shot, currently called Ad26COV2, followed by a second dose or placebo 57 days later, said Saul Faust, a professor of paediatric immunology and infectious diseases who is co-leading the trial at University Hospital Southampton.