Omicron is a coronavirus strain spreading faster than any other.

 The Omicron coronavirus variety is spreading at a rate not observed with earlier versions, according to World Health Organization Director-General Tedros Adhanom Ghebreyesus, who also expressed worry about the tendency to dismiss it as benign.

Tedros stated during a press briefing on Tuesday that the variation has been found in 77 nations.

"The fact is that Omicron is probably in most nations," he noted, "even if it hasn't been discovered yet."

Officials in the United Kingdom have warned that the country is facing a "tidal wave" of Omicron infections. In London, the strain has surpassed the preceding Delta form in dominance.

The first death from the strain was reported in the United Kingdom on Monday. It has raised its Covid-19 warning level once more and is speeding up the deployment of booster doses.

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The United States, as has been the case throughout the epidemic, is lagging behind Europe in assessing the effect of a new variety.

According to the Centers for Disease Control and Prevention, Omicron jumped from accounting for 0.4 percent of circulating virus in the United States in the week ending December 4 to 2.9 percent the next week (CDC).

However, the rates are already substantially higher in the part of the country that includes New York and New Jersey; the CDC believes that Omicron is responsible for 13.1 percent of cases there, compared to only 2 percent the previous week.

Dr. Anthony Fauci, head of the National Institute of Allergy and Infectious Diseases, told CNN on Tuesday that Omicron will become the dominant coronavirus variety in the United States, although it's unknown what that means for severe illness levels.

While research, particularly from South Africa, shows that Omicron may cause milder symptoms than prior variations, public health experts caution that it is too early to draw definite conclusions.

"We're afraid that people are rejecting Omicron as moderate. We must have realized by now that we underestimate this virus at our peril "Tedros said on Tuesday.

"Even if Omicron causes less severe disease, the sheer volume of cases might once again overwhelm unprepared health systems," he noted.

South African experts verified on Tuesday that immunizations give less protection against the new strain, although they noted that they continue to find evidence that Omicron causes milder symptoms than prior versions.

It's unknown why symptoms are milder in South Africa, according to Fauci, but it might be because many people in the population have been infected previously and hence have some kind of immunity.

"Whatever it is, the sickness appears to be less severe; whether it's intrinsically less pathogenic as a virus or if there's greater community protection, we'll just have to see when it comes to the United States," he says.