The US Centers for Disease Control is considering adding a negative test to recommendations on a shortened isolation period for people with asymptomatic infections, President Joe Biden's chief medical adviser said on ABC's "This Week."
US health officials cut the recommended isolation time to five days from 10 after a positive test.
Dr Fauci acknowledged "pushback" to the shortened span without any further test that might indicate if a person is still infected.
Fauci said on CNN, the Omicron variant now sweeping the US may cause milder illness for most, but the sheer number of cases is likely to cause serious sickness in many unvaccinated Americans, and strain health-care resources. "This is a much, much more transmissible virus than Delta is," he said.
Hospital admissions from Covid are rising again in the US, and average daily infections are at a record 400,000, Fauci said.
Studies in the UK have shown that the omicron strain appears less severe than the delta variant it supplanted.
South Africa, where the new variant was identified in November, said last week the omicron-driven wave appears to have passed its peak without a notable rise in deaths.
Almost 73 per cent of US adults are fully vaccinated, and 36.3 per cent have received a booster shot, according to data from the US Centers for Disease Control and Prevention. But coverage varies widely between states.
Fauci said that despite omicron's rapid spread, schools should remain open, though with masking and other rules, and he urged parents to get eligible children vaccinated.
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