Omicron is now dominant Covid-19 variant in US, officials say

Omicron is now the dominant version of the coronavirus in the US, federal health officials said on Monday, racing ahead of Delta and other variants and accounting for 73% of new infections last week.

Since the end of June, the Delta variant has been the main version causing US infections. As recently as the end of November, more than 99.5% of coronaviruses were Delta, according to CDC data.

Much about the omicron variant remains unknown, including whether it causes more or less severe illness. Early studies suggest the vaccinated will need a booster shot for the best chance at preventing omicron infection but even without the extra dose, vaccination still should offer strong protection against severe illness and death.

Adalja said he was not surprised by the CDC data showing omicron overtaking Delta in the US, given what was seen in South Africa, the UK and Denmark. He predicted spread over the holidays, including breakthrough infections among the vaccinated and serious complications among the unvaccinated that could stress hospitals already burdened by Delta.

But CDC on Tuesday said it was revising some of the earlier numbers, after analyzing more specimens. The new numbers indicate that about 13% of the infections the week of 11 December were Omicron, and not 3%, CDC officials said.