Daily Covid cases in the United States have risen to their highest level in more than two months as scientists race to track the spread of the new omicron variant.
Data from Johns Hopkins University of Medicine showed the seven day rolling average for cases per day rising to about 121,437 on 2 December, higher than at any point since 26 September.
Figures showed the US crossing the threshold of 100,000 cases per day on Thursday, having stayed below that level since 6 October.
The vast majority of those infections still probably came from the delta variant, which made up 99.9 per cent of cases in the last week of November according to estimates by the Centers for Disease Control and Prevention (CDC).
Data from the CDC also showed the country’s seven-day average of daily deaths ticking sharply upwards after months of decline, from a low of 731 on 28 November to 1,651 on Saturday.
It comes after cases of omicron were discovered in 16 states across the country, from Hawaii through Colorado to Massachusetts, suggesting that its spread is now unlikely to be contained.
Many of the cases were among people who had been fully vaccinated, although it is not clear whether they had also received booster jabs.
Scientists are still uncertain whether omicron is more contagious or more deadly than delta, with early evidence showing it has 32 new mutations in its spike protein, used by coronaviruses to attack human cells.
Chief White House medical adviser Dr Anthony Fauci told CNN on Sunday that “thus far, it does not look like there’s a great degree of severity to it”, but warned that it was too early to draw conclusions.