Omicron variant now 73% of US Covid-19 cases

US battles testing demands during holiday travel season as 'variant of concern' cases jump from 12% to 73% in seven days

In an aerial view, cars queue at a drive-through Covid-19 testing site at Tropical Park in Miami, Florida. AFP

Live updates: follow the latest news on Covid-19 variant Omicron

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

The Centres for Disease Control and Prevention numbers showed a nearly six-fold increase in Omicron’s share of infections in only one week.

In much of the country, Omicron’s prevalence is even higher, responsible for an estimated 90 per cent of new infections in the New York area, the South-East, the industrial Midwest and the Pacific North-West.

Since the end of June, the Delta variant has been the main variant causing US infections.

As recently as the end of November, more than 99.5 per cent of coronavirus cases were caused by Delta, CDC data show.

Scientists in South Africa first sounded the alarm about Omicron less than a month ago and on November 26, the World Health Organisation designated it as a "variant of concern". The variant has since shown up in about 90 countries.

Much about the Omicron variant remains unknown, including whether it causes more severe illness. Early studies suggest those who have been 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.

“If you’re going to interact with society, if you’re going to have any type of life, Omicron will be something you encounter, and the best way you can encounter this is to be fully vaccinated," said Amesh Adalja, a senior scholar at the Johns Hopkins Centre for Health Security.

Mr 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 it would spread over the holidays, including causing breakthrough infections among the vaccinated and serious complications among the unvaccinated that could stress hospitals already burdened by Delta cases.

The CDC’s estimates are based on thousands of coronavirus specimens collected each week through university and commercial laboratories as well as by state and local health departments. Scientists analyse their genetic sequences to determine which versions of those Covid-19 viruses are most abundant.