Omicron updates: COVID outbreak reported on cruise ship docking in New Orleans

Dr. Ashish Jha, dean of Brown University's School of Public Health, told NBC's "Today" on Monday that he assumes omicron is already in the United States and predicts the new variant be identified in the next few days.

But Jha said he believes it's "extremely unlikely" that omicron would completely evade vaccines.

"I think that our vaccines will hold up -- the question is … is it a little bit less effective? A lot less effective? We will have that data -- both laboratory data and clinical data -- in the next week or two at the most," Jha said.

"I wouldn't make any major changes to plans" for the holidays yet, he continued. "I would just wait and make sure you're vaccinated and everybody around you is vaccinated."

"If you're fully vaccinated -- and especially if you're boosted -- you're going to have more protection against this variant," he said.

-ABC News' Cheyenne Haslett

Portuguese health authorities on Monday confirmed 13 cases of the omicron variant among professional soccer players.

The Ricardo Jorge National Health Institute said the players who tested positive are all members of the Lisbon-based Belenenses SAD soccer club and that one of them had recently traveled to southern Africa, where the omicron variant was first identified last week.

The institute is investigating whether this is one of the first reported instances of local transmission of the new coronavirus variant outside of southern Africa, where most of the cases have been recorded so far.

All 13 players have been placed in quarantine and those who have been in contact with them were ordered to isolate, regardless of their vaccination status or their exposure to possible contagion. The players and their close contacts will be regularly tested for COVID-19, the institute said.

-ABC News' Aicha El Hammar Castano

Moderna's chief medical officer, Dr. Paul Burton, said the omicron variant probably emerged around mid-October in southern Africa.

"How transmissible is it? We think it's probably quite transmissible. But how severe is the disease it causes? We don't know the answer to that question yet," Burton told ABC News' Amy Robach in an interview Monday on "Good Morning America."

"While we think that vaccine effectiveness may come down based on the mutations seen in this virus ... we should be able to get antibodies up" with the booster shot, Burton said.

"We'll know from tests in the next couple of weeks how effective the vaccines are against this variant," he added.

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Moderna's chief medical officer talks omicron variant

Dr. Paul Burton discusses the transmissibility of the omicron variant, the symptoms and whether it's more likely to cause serious illness, and how vaccines might respond to the COVID variant.

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Dr. Anthony Fauci, the U.S. government's top infectious diseases expert, is urging Americans who have been vaccinated against COVID-19 and are eligible to get a booster shot to do so now, in anticipation of the omicron variant spreading "widely."

So far, there are no known confirmed cases of the new variant in the United States, according to Fauci, who is the chief medical adviser to U.S. President Joe Biden.

"But obviously, we're on high alert," Fauci told ABC News' George Stephanopoulos in an interview Monday on "Good Morning America."

"It's inevitable that, sooner or later, it's going to spread widely because it has at least the molecular characteristics of being highly transmissible," he added, "even though there are a lot of things about it that we do not know but will be able to ascertain in the next week or two."

Fauci, who is also the director of the National Institute of Allergy and Infectious Diseases, said omicron clearly has a "transmissibility advantage," based on what scientists have seen in southern Africa, where the variant was first identified last week.

"But the extent of that, again, still needs to be worked out," he noted. "We'll know soon."

Fauci said the severity of illness that the omicron variant can inflict remains unclear, despite early reports that some patients had mild symptoms.

Although there is still so much unknown about the new variant, Fauci said it's clear that vaccinated individuals, particularly those who have received booster doses, fare better against COVID-19 than their unvaccinated counterparts.

"So we don't know exactly what's going on with this new variant," he said, "but I would assume -- and I think it's a reasonable assumption -- that when you get vaccinated and boosted and your [antibody] level goes way up, you're going to have some degree of protection, at least against severe disease."

Both Pfizer-BioNTech and Moderna booster shots have been authorized for all adults in the United States. Anyone over the age of 18 can get a booster dose at least six months after they received their second dose of the Pfizer-BioNTech or Moderna vaccines, or at least two months after they got their single dose of the Johnson & Johnson vaccine.

"I would strongly suggest you get boosted now and not wait for the next iteration of [the vaccine], which we may not even need," Fauci said. "The pharmaceutical companies are preparing to make a specific booster for [omicron], but we may not need that."

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US braces for 'inevitable' arrival of omicron variant

Scientists said the variant, first detected in southern Africa, has a concerning combination of mutations and cases have been confirmed in at least 13 countries.

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