Live updates: follow the latest news on Covid-19 variant Omicron
The US has hit its highest-ever average of new coronavirus cases as the Omicron variant spreads at a blistering pace, amid testing woes and health worker shortages.
The moving seven-day average of new cases was 265,427 as of Tuesday, surpassing the previous peak of 251,989 set in mid-January 2021, a tracker maintained by Johns Hopkins University showed.
The heavily mutated Omicron strain, which according to government modelling accounted for around 59 percent of national US cases in the week ending December 25, is the most transmissible seen to date.
It is frequently able to bypass immunity conferred by vaccination and prior infection.
Though the rate of severe outcomes appears to be lower, Omicron is already stretching previously strained hospital systems throughout the country, with health workers leaving in droves because of burnout.
Still, with many testing centres closed for the holidays, the total number of cases may not be known until later because of a delay in state reporting.
Nationwide, almost 9,000 Covid patients are being admitted every day, according to data collected by the US Centres for Disease Control and Prevention (CDC), still some way short of the peak of 16,500 per day seen in January, though this is a lagging indicator.
Around 1,200 people were dying on average every day on December 23, the day before data collection was disrupted by Christmas holidays.
In January, deaths peaked at an average of 3,400 a day.
Paediatric hospital admittances are, however, rising nationwide — nearing a peak experienced earlier this fall, when the Delta variant hit the younger unvaccinated population hard.
Children under the age of five are still ineligible to be vaccinated.
More than 820,000 Americans have died from Covid-19, making the US the hardest-hit country in the world in terms of numbers, ahead of Brazil and of India.
By October, the latest month for which data has been analysed, unvaccinated people had a five times greater chance of being infected with Covid, and 14 times higher chance of dying, compared to vaccinated people.
Though those data do not account for Omicron, accumulating research shows that vaccination and boosting continue to protect well against severe outcomes.
The latest milestone comes as the CDC shortened recommended times that people should isolate after a positive test from 10 to five days, so long as they do not have symptoms and continue to wear a mask.
The move was praised by airlines and the hospitality industry, but public health experts criticised the decision to omit a requirement for a negative Covid test — even via rapid antigen, which correlates well with infectiousness.
Adding to confusion, the CDC on Tuesday revised its Omicron case projection in the US. The health agency estimated Omicron's proportion of cases for the week ending December 18 to 22 per cent, down from 73 per cent.
The Omicron variant currently accounts for 58.6 per cent of cases circulating in the US, according to data from the CDC.
Agence France-Presse contributed to this report