US health authorities have halved the recommended isolation time for people with asymptomatic Covid-19, as President Joe Biden warned Americans not to panic amid a surge of cases threatening wider social disruption.

The CDC recommendations, which cut isolation for asymptomatic cases from 10 to five days, open the way for people to return to work sooner — minimising the prospect of mass labour shortages in key parts of the economy.

The recommendations, which are non-binding but closely followed by US businesses and policymakers, further suggest that the five-day isolation period be “followed by five days of wearing a mask when around others”, AFP reported.

The agency said the new guidelines were “motivated by science”, which had demonstrated that the majority of Covid-19 transmission occurs early in the course of illness, generally one to two days prior to the onset of symptoms and in the two to three days after.