• Fauci blamed the increasing number of Covid cases on the roughly 60 million eligible individuals across the country who remain unimmunized against the virus.
• He referenced Israeli data that showed Covid booster doses lowered recipients' chances for infection and severe symptoms.
• Some 30.1 million people nationwide have received an additional dose of a Covid vaccine, the CDC reported as of Monday.

White House chief medical adviser Dr. Anthony Fauci is calling on eligible Americans to get their Covid-19 booster shots as the holiday season approaches and cases rise nationwide, driven by upticks in the Midwest and Northeast.

Fauci blamed the increasing cases on the roughly 60 million eligible individuals across the country who remain unimmunized against the virus. The Centers for Disease Control and Prevention also expanded access to Pfizer's two-dose vaccine to approximately 28 million children ages 5 to 11 earlier this month after approving booster doses for almost 100 million people this fall.

"Always the primary thing is to get the unvaccinated vaccinated," Fauci said in an interview on "The News with Shepard Smith" Monday night. "But for those who are eligible to be boosted, by all means, go and get boosted."

Fauci referenced Israeli data that showed Covid booster doses lowered recipients' chances for infection and severe symptoms. Researchers in Israel also demonstrated the waning effectiveness of Pfizer and BioNTech's Covid shots in a study of nearly 4.8 million vaccinated adults, with higher rates of infection across all age groups among those who completed their second shot in mid-January compared to those who became fully vaccinated in February and March.

Some 30.1 million people nationwide have received an additional dose of a Covid vaccine, the CDC reported as of Monday. Boosters are available for select Pfizer and Moderna recipients, including anyone 65 and older, all adults with medical conditions that cause Covid complications, adults living or working in congregate settings and any front-line worker 18 and older at high risk for exposure to the virus.

But anyone who received Johnson & Johnson's one-dose vaccine is eligible for a booster regardless of their medical or occupational risks.

Fauci's comments came hours after he discussed the rise in Covid cases affecting select regions in an interview with the Bipartisan Policy Center. The U.S. recorded a seven-day average of over 82,000 new cases Sunday, up 11% from the week prior, according to a CNBC analysis of data from Johns Hopkins University.

Average cases have climbed 37% in the Northeast and 19% in the Midwest over the last seven days, JHU reported. The country's case count last week was 57% lower than the peak of this summer's delta surge, with infections plateauing between 70,000 and 75,000 per day for more than two weeks before experiencing three consecutive days of increases beginning Friday.

CNBC's Nate Rattner contributed to this reporting.