In an interview last week with The New York Times published on Thursday, infectious disease expert Dr. Anthony Fauci admitted he was not completely honest about the percentage of Americans who needed to get the coronavirus vaccine before the American population can reach herd immunity.

At the beginning of the pandemic, Fauci said 60-70% of the American public would need to receive the vaccine to reach herd immunity, but as more Americans became wary of the vaccine, Fauci slightly increased his percentages, telling the Times that achieving herd immunity would require 90% of the American public to receive the vaccine.

“When polls said only about half of all Americans would take a vaccine, I was saying herd immunity would take 70 to 75 percent … Then, when newer surveys said 60 percent or more would take it, I thought, ‘I can nudge this up a bit,’ so I went to 80, 85. We need to have some humility here …. We really don’t know what the real number is. I think the real range is somewhere between 70 to 90 percent. But, I’m not going to say 90 percent,” Fauci said.

Fauci defended his statements on CNN’s “State of the Union” on Sunday, saying he made a “guesstimate.”

“I want to encourage the people of the United States and globally to get vaccinated, because, as many as we possibly get vaccinated, we will get closer to herd immunity. So, the bottom line is, it’s a guesstimate,” Fauci said.

Fauci said he based his numbers on measles, not polling.

“It was really based on calculations and pure extrapolations from measles,” Fauci said.

“Measles is about 98% effective vaccine, the COVID-19 vaccine is about 94-95%. When you get below 90% of the population vaccinated with measles, you start seeing a breakthrough against the herd immunity, people starting to get infected, like we saw in upper New York State and in New York City, with the Orthodox Jewish group, when we had the measles outbreak,” he continued.

“So, I made a calculation that COVID-19, SARS-CoV-2, is not as nearly as transmissible as measles. Measles is the most transmissible infection you can imagine. So, I would imagine that you would need something a little bit less than the 90%. That’s where I got to the 85.”