The paper defines "long Covid" as having symptoms persist for more than four weeks, while a short duration of Covid was defined as less than 10 days, without a subsequent relapse.

About 1 in 20 people with Covid-19, or 4.5%, are likely to experience symptoms for eight weeks or more, the preprint analysis of data from the Covid Symptom Study app showed.

Claire Steves, clinical academic and senior author from King's College London, in a news release.

While most of the people with Covid-19 in the study reported being back to normal in 11 days or less, about 1 in 7 reported symptoms lasting for at least four weeks, about 1 in 20 for at least eight weeks and about 1 in 50 for at least 12 weeks.

Long Covid sufferers were also twice as likely to report a relapse after they recovered compared with those who had "short Covid" (16% vs 8.4%).

About 1 in 5 adults older than 70, or 21.9%, who tested positive for coronavirus developed long Covid, compared with about 1 in 10 18- to 49-year-olds, the study found.