US health officials have halved the recommended isolation time for people with asymptomatic Covid-19 from 10 to five days, amid a surge in cases.
The measure is expected to alleviate disruption caused by staff shortages in many areas because of infections.
The Centers for Disease Control (CDC) says most transmissions happen in the two days before and three days after symptoms develop.
But experts have criticised the lack of testing requirements to end isolation.
The sharp rise in cases has been fuelled by the Omicron variant of the virus, which is now dominant in the US. Early studies suggest Omicron is more contagious than other variants, although milder.
The growing number of people having to isolate has put pressure on several industries, including air travel, with thousands of flights cancelled during the Christmas holiday.
Leaders of major US airlines were among those calling for the change, as cancellations continued for a fourth day on Tuesday.
The CDC said the new guidance was "motivated by science", and that the isolation must be followed by five days of wearing a mask around others. The announcement came as more than 200,000 daily infections were confirmed in the past two days nationwide.
CDC director Dr Rochelle Walensky said the recommendation "balances what we know about the spread of thevirus and the protection provided by vaccination and booster doses".
.jpg)
