The Omicron variant of the coronavirus has spread to at least 19 U.S. states but seems less severe than the Delta variant, though more time is needed to gain a fuller picture, top U.S. health officials said on Tuesday.

"It's too early to be able to determine the precise severity of disease, but inklings that we are getting, and we must remember these are still in the form of anecdotal ... but it appears that with the cases that are seen, we are not seeing a very severe profile of disease," said Anthony Fauci, chief medical advisor to the U.S. president, during a White House briefing.

The new variant was first reported to the World Health Organization (WHO) from South Africa on November 24. It has spread across several countries in a short time. 

A total of 57 countries and regions have so far reported Omicron, mostly related to travel, the WHO said on Tuesday. But the Delta variant remains the most popular one in many countries, it continued. 

Although scientists are still studying the variant and its effects, a WHO official told AFP on Tuesday that Omicron does not appear to cause more severe disease than previous variants and is "highly unlikely" to fully dodge vaccine protections.

"The preliminary data doesn't indicate that this is more severe. In fact, if anything, the direction is towards less severity," WHO emergencies director Michael Ryan said in an interview, insisting that more research was needed. "It's very early days; we have to be very careful how we interpret that signal."

"We have highly effective vaccines that have proved effective against all the variants so far in terms of severe disease and hospitalization," he said. "There's no reason to expect that it wouldn't be so" for Omicron.

A recent analysis released by the National Public Radio (NPR) on Sunday said that people living in pro-Trump counties have a COVID-19 death rate nearly three times higher than those living in counties that voted for Joe Biden, with low vaccination being a major reason.

"The higher the vote share for Trump, the lower the vaccination rate," the NPR data revealed.

(With input from agencies)