Dr. Anthony Fauci, director of the National Institute of Allergy...

Dr. Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases, speaks during a briefing at the White House on Dec. 1. Credit: AP / Susan Walsh

Top federal health officials warned Sunday that Americans face "a tough few weeks" ahead as the "very contagious" omicron coronavirus variant spreads at an unprecedented rate before the Christmas and New Year’s holidays.

Chief White House medical adviser Dr. Anthony Fauci said on CNN he expects the United States to see record numbers of cases, hospitalizations and deaths from the omicron variant.

Omicron doubles its spread in two to three days, partly due to a higher-than-expected number of mutations, he said.

That transmission rate shows omicron probably is "overtaking all the other variants" and is "really something to be reckoned with," Fauci said on ABC’s "This Week."

In South Africa, where scientists first detected the variant, early data shows "encouraging signs" that omicron may not lead to as many hospitalizations, said Dr. Francis Collins, the outgoing director of the National Institutes of Health.

But officials are "just sort of holding our breath to see how severe the cases will be" in the United States, especially for people who are not vaccinated against the virus, have underlying medical conditions or are over age 65, Collins said.

Fauci warned on CNN’s "State of the Union" that "it is going to be a tough few weeks to months as we get deeper into the winter."

About 50 million people who are eligible for the vaccine are not vaccinated, which probably will put a strain on hospital systems and "health care workers who are getting exhausted."

"I don't foresee the kind of lockdowns that we've seen before, but I certainly see the potential for stress on our hospital system," Fauci said on ABC.

People who are not vaccinated should not travel for the holidays "because you are in a very vulnerable place with omicron," Collins said.

Fauci and Collins urged people to get vaccinated and get booster shots.

Even those who are vaccinated should wear masks in indoor settings and ask guests to take rapid tests before any holiday gathering.

"Nothing is 100% risk-free, but I think if you do the things that I just mentioned, you’d actually mitigate that risk enough to feel comfortable about being able to enjoy the holiday," Fauci said on ABC, noting that just getting vaccinated isn't enough.

Also complicating the fight against COVID-19 this winter: a lack of enough rapid tests, the delay of vaccine approval for kids under age 5 and an expected monthslong wait for a COVID-fighting pill to become widely available.

Fauci said the federal government is spending billions of dollars to produce between 200 to 500 million rapid tests a month, which should make them more widely available in the next couple of weeks.

Those tests are expected to accurately detect the omicron variant as the federal Food and Drug Administration re-examines some PCR tests to ensure they do, too.

One potential for normalcy this winter: children won't have to quarantine and stay out of school if they continue to test negative for the virus after potential exposure, under new guidance from the U.S. Centers for Disease Control and Prevention, Fauci said.

Collins acknowledged Sunday that people listening to him probably think, " ‘I am so sick of hearing this.’ "

"And I am too, " he added. "But the virus is not sick of us, and it is still out there looking for us, and we've got to double down on these things if we're going to get through the next few months."

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