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.

Dr. Anthony Fauci, the top U.S. infectious disease expert, said Monday the nation should consider a vaccination mandate for domestic air travel, signaling a potential embrace of an idea the Biden administration has previously eschewed, as COVID-19 cases spike.

Fauci, President Joe Biden’s chief science adviser on the pandemic response, said such a mandate might drive up the nation’s lagging vaccination rate as well as confer stronger protection on flights, for which federal regulations require all those age 2 and older to wear a mask.

“When you make vaccination a requirement, that’s another incentive to get more people vaccinated,” Fauci told MSNBC. “If you want to do that with domestic flights, I think that’s something that seriously should be considered.”