CDC: people who test positive for Covid with no symptoms should isolate just five days

US health authorities have halved, to five days, the recommended isolation time for people with asymptomatic Covid.

The US is facing a huge surge in Covid cases, driven by the Omicron variant, which contributed to travel chaos over Christmas and stoked worries about damage to the economy and education.

The CDC said that after isolation, asymptomatic people should wear a mask around others for another five days.

It also recommended a five-day quarantine for those exposed while unvaccinated, more than six months out from their second dose or more than two months out from a single-dose Johnson & Johnson shot and not yet boosted.

Others pointed to the need to avoid significant disruption to daily life.

Amid cancellations caused in part by Omicron, Anthony Fauci said a mandate might confer stronger protection on flights, for which federal regulations require all those aged two and older to wear a mask.

Two officials told the Associated Press advisers had yet to make a recommendation, as a mandate could trigger logistical and legal concerns.

At the White House, Biden told reporters the subject was discussed with governors.

Biden pledged full federal support to states facing Omicron and a run on tests.

Earlier this year, the White House explored a domestic vaccination requirement for flights, or requiring vaccination or a negative test. Officials expected legal challenges.

The CDC says more than 241 million Americans, about 77% of the eligible population aged five and over, have received at least one shot. The administration has instituted requirements that federal workers, contractors and those in healthcare get shots, and that companies with 100 or more employees have vaccination or testing mandates.

Those moves have been mired in legal wrangling. The supreme court is set to hear arguments on 7 January.

Such legal moves are likely to play out amid more distressing scenes nationwide.

Michael Osterholm, director of the Center for Infectious Disease Research and Policy at the University of Minnesota, told the Times the national character of the Omicron surge meant resources would be stretched and healthcare workers hit hard.