If the U.S. allowed the coronavirus to spread unchecked in an attempt to try to achieve so-called herd immunity, the “death toll would be enormous,” White House coronavirus advisor Dr. Anthony Fauci warned on Thursday. 

“If everyone contracted it, even with the relatively high percentage of people without symptoms … a lot of people are going to die,” Fauci, the director of the National Institute of Allergy and Infectious Diseases, told actor Matthew McConaughey during a live discussion on Instagram. 

According to epidemiologists, herd immunity is necessary to contain a virus and is reached when enough of the population is either vaccinated or survive infection and build antibodies to ward of new infections. The virus then doesn’t have enough hosts to infect. 

Most scientists think 60% to 80% of the population needs to be vaccinated or have natural antibodies to achieve herd immunity, Dr. Mike Ryan, executive director of the World Health Organization’s health emergencies program, said last month.

The coronavirus, however, has infected less than 2% of the U.S. population and has already killed at least 166,970 people, according to Johns Hopkins University data. Letting the virus spread uncontrollably to achieve herd immunity would bring the death toll to a level that’s “totally unacceptable,” Fauci said. Americans tend to have more underlying conditions, like diabetes and obesity, that lead to higher death rates from the coronavirus.

“If you look at the United States of America with our epidemic of obesity as it were, with the number of people with hypertension, with the number of people with diabetes, if everyone got infected, the death toll would be enormous and totally unacceptable,” Fauci said. 

“And that’s the reason why we’re against saying ‘Let it fly! Let everybody get infected and we’ll be fine.’ That’s a bad idea,” he added. 

WHO officials have also advised public officials against trying to achieve herd immunity by allowing Covid-19 to rapidly spread throughout their communities. Organization officials have said it would overwhelm hospitals and kill a lot of people.

“We’re nowhere near close to (herd immunity), which means this virus has a long way to burn in our communities before we ever reach that,” Ryan said. 

Infectious disease experts, including Fauci, maintain that it’s unlikely the coronavirus will ever be eradicated, though nations can bring the level of infection down to “low levels.” 

“I think with a combination of good public health measures, a degree of global herd immunity and a good vaccine, which I do hope and feel cautiously optimistic that we will get, I think when we put all three of those together, we will get control of this, whether it’s this year or next year. I’m not certain,” Fauci told the TB Alliance on July 22. 

— CNBC’s Berkeley Lovelace Jr. contributed to this report.