As the number of positive COVID-19 cases continues to rise in the U.S., fueled by the more transmissible Delta variant, Dr. Anthony Fauci said Sunday that unvaccinated Americans are responsible for the spread.

Fauci, the nation's top infectious disease doctor, discussed the increase of cases and slow in vaccinations during an appearance on CBS News' “Face the Nation.”

“We have 100 million people in this country who are eligible to be vaccinated who are not getting vaccinated,” Fauci said.

“We’ve really got to get those people to change their minds, make it easy for them, convince them, do something to get them to be vaccinated because they are the ones that are propagating this outbreak.”

Around 58% of Americans have received at least one dose of the COVID-19 vaccine, but there are still millions of people who are not protected from the virus. 

However, since more than half of Americans have received the vaccine, Fauci believes it will help avoid a massive shutdown. 

“Not enough to crush the outbreak, but I believe enough to not allow us to get into the situation we were in last winter,” he said.

Fauci added that he expects “things are going to get worse” amid the spread of the Delta variant.

The Centers for Disease Control and Prevention issued an updated mask guideline last week, advising both vaccinated and unvaccinated people to wear face coverings indoors.

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