Speaking at the White House COVID-19 response team briefing, Fauci said the U.S. is looking over its shoulder at oncoming omicron infections.
"We are in a situation: we are now facing a very important delta surge and we are looking over our shoulder at an oncoming omicron surge," he said.
"Clearly, unvaccinated individuals … are really at a high risk of serious involvement, including hospitalization. The fully vaccinated are doing much better off but, as I've shown you … the optimum protection is fully vaccinated plus a boost," Fauci added.
Centers for Disease Control and Prevention (CDC) Director Dr. Rochelle Walensky announced that the seven-day average of hospital admissions had increased by about 4% and deaths had increased by more than 8% from the prior week.
"Although delta continues to circulate widely in the United States, omicron is increasing rapidly and we expect it to become the dominant strain in the United States – as it has in other countries – in the coming weeks," she said. "We've seen cases of omicron among those who are both vaccinated and boosted and we believe these cases are milder or asymptomatic because of vaccine protection."
"What we do know is we have the tools to protect ourselves against COVID-19," the Walensky noted, echoing previous comments by White House COVID-19 response coordinator Jeff Zients.
Zients said the administration was intent on not letting omicron disrupt work in school for the vaccinated, but said the unvaccinated are looking at a "winter of severe illness and death."
"We are prepared to confront this new challenge," he pledged, adding that while "this is not a moment to panic," the American people need to do their part.
CDC data shows that more than 203 million Americans have been fully vaccinated and more than 57 million have received a booster dose since Aug. 13.
The Johns Hopkins Coronavirus Resource Center shows that more than 50 million cases have been confirmed in the U.S. and more than 800,000 people have died from the virus.
Recently, many states have seen cases and hospitalizations climb and major universities have reported large COVID-19 outbreaks – including omicron cases. The variant has been detected in 39 states and CDC estimates suggest 3% of cases nationally involve the new variant.
In a Thursday interview on the U.S. Chamber of Commerce Foundation's "Path Forward," Fauci said the variant's transmissibility ensured its dominance.
"There are few things we know for certain and a couple of things that we can make a rather reasonable assumption about," he said. "The first that we know for sure: that it is highly, highly transmissible. It is the most transmissible virus of COVID that we've had to deal with thus far. It has a doubling time of about three days which means, if you do the math on that, you see how quickly over a period of time that the dominant variant will be omicron – as it is in South Africa, as it is now approaching that in the U.K. And, if things go in the United States the way they've gone in other countries – and there's no reason to believe that that won't be the case – it will soon become dominant here."
The infectious disease expert also pointed out that the large number of mutations on the omicron variant is predictive and has shown in reality to evade certain immune parameters, such as monoclonal antibodies.
With omicron, antibodies induced by vaccination lose much of their potency, although Fauci noted that those who have been fully vaccinated and boosted can "reconstitute a lot of that diminished protection."
"It may not protect much against infection, but it will go a long way to protect against severe disease. So, therefore underscoring the real importance of getting vaccinated, as well as getting boosted," he continued, next underscoring the importance of not making assumptions regarding its severity.
All of this comes amidst what Fauci said is a difficult situation, due to the 50 million Americans who remain unvaccinated.
"The very vulnerable people … are predominantly … the unvaccinated," he explained. "And that's the reason why as we get into the depths of the winter with the travel and the holiday season upon us, that it is essential to get the unvaccinated people vaccinated. And importantly, particularly, with regard to omicron…"
Hospitals, he added, could be overwhelmed in the coming months – though he said he would not object to family gatherings for the holidays, if people are vaccinated.