The nation’s leading infectious disease expert is concerned that a deadlier COVID variant could be on the horizon if more people don’t get vaccinated.

Dr. Anthony Fauci shared the warning in a Wednesday interview with McClatchy, where he expressed his concern for the “steep” increase in Delta variant cases, which he expects to double in the coming weeks to 200,000 cases a day.

He told the news outlet that the U.S. could be “in trouble” as it enters the fall unless a large portion of unvaccinated Americans decided to get their shots.

The head of the National Institute of Allergy and Infectious Diseases continued by saying, “What we’re seeing, because of this increase in transmissibility, and because we have about 93 million people in this country who are eligible to get vaccinated who don’t get vaccinated — that you have a significant pool of vulnerable people.

“And so when you look at the curve of acceleration of seven-day averages of cases per day, it is going up in a very steep fashion.”

At the height of the pandemic, the U.S. reported 295,880 positive cases of COVID on a single day on Jan. 7, McClatchy reported. This number had declined to 8,069 by June 14. As of Aug. 2, the seven-day rolling average of daily positive COVID-19 cases was 84,389, according to the Centers for Disease Control and Prevention.

Fauci, who is also the chief medical advisor to President Joe Biden, maintained that while the Delta variant is highly contagious, the virus can still get worse, citing his fears of a more “ample” morph of a more deadly strain of COVID-19 that evades the vaccine.

“If we don’t crush the outbreak to the point of getting the overwhelming proportion of the population vaccinated, then what will happen is the virus will continue to smolder through the fall into the winter, giving it ample chance to get a variant which, quite frankly, we’re very lucky that the vaccines that we have now do very well against the variants — particularly against severe illness,” Fauci said. “We’re very fortunate that that’s the case. There could be a variant that’s lingering out there that can push aside Delta.

“If another one comes along that has an equally high capability of transmitting but also is much more severe, then we could really be in trouble,” he said. “People who are not getting vaccinated mistakenly think it’s only about them. But it isn’t. It’s about everybody else, also.”

Others have echoed Fauci’s warning to the unvaccinated.

Michael Osterholm, director for the Center for Infectious Disease Research and Policy at the University of Minnesota, told CNN, "This virus is highly infectious. If you decide to try to run the game clock out, don't try to do it. This virus will find you, it will infect you eventually.

"If that's not enough to motivate people to get vaccinated then the only other things I think we have are the mandates that say, 'If you're going to work here or go have to get vaccinated.'"

Osterholm added that the unvaccinated are not only putting themselves at risk by not getting their COVID-19 shot, but they are also putting everyone around them in danger.

"If you are a case and you become infectious, you do two things: one is you pose a risk to others including your own loved ones, but number two is you're also using hospital resources right now which in many instances are very, very short," he told CNN.

According to the CDC, over 165 million people have been fully vaccinated against COVID-19, representing 49.8% of the U.S. population. More than 90 million eligible Americans are still unvaccinated, CNN said.

Top US disease expert Anthony Fauci
Top U.S. disease expert Dr. Anthony Fauci is seen speaking to a New York church group on June 6, 2021. GETTY IMAGES NORTH AMERICA / Jeenah Moon