National Institute of Allergy and Infectious Diseases head Anthony Fauci on Sunday said it could be weeks or months before life in the U.S. goes "back to normal" but that the worst-case scenario projections of coronavirus infections and deaths are unlikely to materialize.

Fauci, one of the faces of the Trump administration's response to the coronavirus outbreak, appeared on all five of the Sunday morning political shows to provide updates on the spread of COVID-19 and counsel Americans on the steps they should take to mitigate it.

“If you just leave the virus to its own defenses it’ll go way up like we’ve seen in Italy – that’s not going to happen if we do what we’re attempting to do and are doing,” Fauci told CBS’ Margaret Brennan on “Face the Nation.”

Fauci's appearances came soon after the Centers for Disease Control and Prevention (CDC) reportedly determined that the worst-case scenario for the virus could involve up to 214 million infections and 1.7 million deaths.

That's unlikely to happen in the U.S. as long as serious precautions continue, Fauci said.

“The worst-case scenario is either you do nothing or your mitigation and containments don't succeed,” Fauci told Karl. “So although that's possible, it is unlikely if we do the kinds of things that we're essentially outlining right now.”

Steps taken across the U.S. have included recommendations that people stay home, avoid large gatherings and minimize traveling. Cities and states across the country have banned large gatherings and sports events, festivals and concerts have been canceled. The administration is also implementing a travel ban from Europe, China and Iran; U.S. residents returning home are exempt.

“[Y]ou block infections from coming in, and then within is when you have containment and mitigation,” Fauci said. “And that's the reason why the kinds of things we're doing that may seem like an overreaction will keep us away from that worst-case scenario.”

Fauci also warned that while the greatest threat from the virus is believed to be to elderly people and those with underlying medical conditions, young people should be aware of the risk to themselves as well.

"Younger people should be concerned for two reasons. You are not immune or safe from getting seriously ill” and younger patients can still act as carriers for the virus, Fauci said on CNN’s “State of the Union.”

"You can bring it to a person, who can bring it to person, who can bring it to your grandmother or grandfather or elderly relative," he added.

Although some countries hit particularly hard by the virus, including Italy, have imposed domestic travel restrictions to prevent its spread, Fauci said he doubted such a step would be taken in the U.S.

He also addressed large crowds of returning travelers that were seen at major U.S. airports like Chicago’s O’Hare International Airport over the weekend, saying “we’d like to not see crowds like that.”

“I think people understand if you’re an American citizen, if you are a family member, that you can get back, you don’t need to rush back,” he told Fox News’ Chris Wallace Christopher (Chris) WallaceBiden town hall draws 3.3 million viewers for CNN Gates says travel ban made COVID-19 worse in US CNN slammed for soft questions during Biden town hall: 'The media is broken' MORE. “But it’s understandable if when people see a travel ban, they immediately want to ... get home.”

Other administration officials also addressed the outbreak Sunday, with Treasury Secretary Steven Mnuchin Steven Terner MnuchinLawmakers fear voter backlash over failure to reach COVID-19 relief deal United Airlines, unions call for six-month extension of government aid House Democrats plan to unveil bill next week to avert shutdown MORE and White House Economic Council Director Larry Kudlow Larry KudlowMORE discussing its economic implications.

Mnuchin, appearing on “Fox News Sunday,” told Wallace he expected the economy to make a “big rebound” despite the downturn caused by the virus.

“What I’d focus on is what do we need to do right now because it’s clear we need to get economic relief to the economy right now,” Mnuchin said on “Fox News Sunday.” “If the medical professionals are correct and we’re doing all the things, I expect we’ll have a big rebound later in the year.”

Kudlow, meanwhile, said most U.S. supply lines were working “pretty well” amid the pandemic. “Most of our supply lines are working pretty well in the domestic United States … there’s a huge economic challenge here, don’t get me wrong—on the other hand, most of America is still working,” he said on CBS’ “Face the Nation,” but added “the employment story may become more tenuous in the weeks ahead.”