British scientists on Monday launched a trial which will deliberately expose participants who have already had Covid-19 to the coronavirus again to examine immune responses and see if people get reinfected.

In February, Britain became the first country in the world to give the go-ahead for so-called "challenge trials" in humans, in which volunteers are deliberately exposed to Covid-19 to advance research into the disease caused by the coronavirus.

The study launched on Monday differs from the one announced in February as it seeks to reinfect people who have previously had Covid-19 in an effort...