WHO warns Omicron is spreading faster than any other coronavirus variant

The Omicron coronavirus variant is spreading at a rate not seen with previous variants, World Health Organization Director-General Tedros Adhanom Ghebreyesus has warned, adding that the tendency to dismiss it as mild is concerning.

Speaking during a news conference on Tuesday, Tedros said the variant has been detected in 77 countries.

"The reality is that Omicron is probably in most countries, even if it hasn't been detected yet," he added.

Officials in Britain have warned the country is facing a "tidal wave" of infections from Omicron. The strain has become dominant in London, outcompeting the previous Delta variant.

On Monday, the UK reported its first death from the variant. It has once again increased its Covid-19 alert level and is accelerating the rollout of booster shots.

As has been the case throughout the pandemic, the United States is running behind Europe in seeing the impact of a new variant.

Omicron went from accounting for 0.4% of circulating virus in the US in the week to December 4 to 2.9% the following week, according to the Centers for Disease Control and Prevention (CDC).

But the rates are already much higher in the region of the country containing New York and New Jersey, The CDC estimates 13.1% of cases there are caused by Omicron, compared to just 2% in the previous week.

Dr. Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases, told CNN on Tuesday that Omicron will become the dominant coronavirus variant in the US , but it's unclear what that will mean for levels of severe disease.

While data, especially from from South Africa, suggests Omicron might be causing milder symptoms than previous variants, public health experts stress it's too early to make firm conclusions.

"We're concerned that people are dismissing Omicron as mild. Surely, we have learned by now that we underestimate this virus at our peril," Tedros said on Tuesday.

"Even if Omicron does cause less severe disease, the sheer number of cases could once again overwhelm unprepared health systems," he added.

South African researchers confirmed Tuesday that vaccines provide less protection against the new strain but added that they still see indications that Omicron causes milder symptoms than previous variants.

Fauci said it is unclear why symptoms are milder in South Africa, but it could be because many in the community have been infected before so have some level of protection.

"Whatever it is, the disease seems to be less severe, whether it's inherently less pathogenic as a virus, or whether there's more protection in the community, we're just going to have to see when it comes in the United States," he said.