• White House chief medical advisor Dr. Anthony Fauci said 226 cases of the omicron Covid variant have been detected across 20 countries so far but officials haven't confirmed a case in the U.S. yet.
• The variant, which emerged from South Africa about a week ago, has more than 30 mutations to the spike protein alone. That's the key part of the virus that allows it to bind to human cells and infect the body.
• "This mutational profile is very different from other variants of interest and concern," Fauci said. "These mutations have been associated with increased transmissibility and immune evasion."

White House chief medical advisor Dr. Anthony Fauci said Tuesday that 226 cases of the highly mutated omicron Covid-19 variant have been detected across 20 countries so far but officials haven't confirmed a case in the U.S. yet.

The variant, which emerged from South Africa about a week ago, has more than 30 mutations to the spike protein alone. That's the key part of the virus that allows it to bind to human cells and infect the body. It also makes scientists worry that it could evade vaccine protection or may be far more infectious than the already highly contagious delta variant, which has caused a surge in cases across globe in recent months.

"This mutational profile is very different from other variants of interest and concern, and although some mutations are also found in delta, this is not delta," Fauci told reporters on a White House Covid task force briefing. "These mutations have been associated with increased transmissibility and immune evasion."

He said the virus has several other mutations that scientists haven't seen before and that scientists don't know how those mutations will change the way the virus behaves or spreads.

Moderna CEO Stephane Bancel warned Monday that omicron has already spread across the planet. He pointed to flights that arrived in Amsterdam from South Africa on Friday in which 61 of 624 passengers tested positive for Covid. Dutch health authorities said 14 of them are infected with the omicron strain.

Portuguese health authorities said Monday that 13 members and staff of a professional soccer team in Lisbon were infected with the variant after one of its players returned from a trip to South Africa.

"We also believe it is already present in most countries," Bancel said in an interview on CNBC. "I believe most countries that have direct flights from South Africa in the last seven to 10 days already have cases in their country that they may not be aware of."

U.S. officials are stepping up surveillance of international travelers at airports and holding regular, even daily, calls with state and local health officials, lab directors, state epidemiologists and others, looking for omicron cases, said Dr. Rochelle Walensky, director of the Centers for Disease Control and Prevention.

The nation also has stepped up genomic sequencing of Covid cases in recent months, sequencing about 80,000 samples per week, up from about 8,000 per week earlier this year, Walensky said at the briefing. The delta variant remains the predominant strain in the U.S., accounting for about 99.9% of all cases sequenced across the country, she said.

"To be crystal clear, we have far more tools to fight the variant today than we had at this time last year," Walensky said.

Fauci said it's too early to tell whether omicron will be more deadly or mild than the delta variant. He noted that reports of milder symptoms in South Africa were based on a small number of cases and occurred in younger and healthier patients, whose Covid symptoms would typically be milder. The population in the U.S. and Europe tends to be older and less healthy than South Africa's population, Moderna's Bancel said.

"It is very difficult to know whether or not this particular variant is going to result in severe disease," Fauci said. "Although some preliminary information from South Africa suggests no unusual symptoms associated with [this] variant, we do not know and it is too early to tell."

The officials reiterated their push for vaccinations and other prevention measures.

"How do we address omicron? We've said it over and over again, and it deserves repeating, if you're not vaccinated, get vaccinated. Get boosted if you are vaccinated. Continue to use the mitigation methods, namely masks, avoiding crowds and poorly ventilated spaces," Fauci said.

The CDC strengthened its recommendations on Covid boosters Monday, saying everyone 18 and over should get one.

Walensky said the CDC's definition of "fully vaccinated" hasn't changed. It's still two weeks after the second shot of Moderna's or Pfizer's vaccine or one shot of Johnson & Johnson's. But she said the more the virus mutates, the greater the need to bolster immunity. "As that science evolves, we will look at whether we need to update our definition of fully vaccinated," she said.