The majority of people who have had Covid-19 are protected from getting it again for at least six months, a study published on Wednesday showed, but older people are more prone to reinfection than younger people.

The study, appearing in the Lancet medical journal, found that just 0.65 percent of patients tested positive a second time for Covid-19 after previously being infected during Denmark's first and second waves. That was much lower than the 3.27 percent who were positive for the virus using highly accurate PCR tests after initially being negative...