Fact-checking Sen. Rubio's criticism of Dr. Fauci

"Dr. Fauci lied about masks in March," Rubio tweeted on Sunday morning. "Dr. Fauci has been distorting the level of vaccination needed for herd immunity."

Facts First: Rubio's claims are false and misleading. Fauci did not lie about masks. Though Fauci, along with several other US health leaders, did initially advise people not to wear masks, his guidance evolved along with the scientific community's understanding of the coronavirus. Similarly, Fauci has insisted any change in the numbers he's provided regarding herd immunity is due in large part to new science and representative of the fact that there's a range of estimates for the necessary level.

On vaccines

There is some basis for Rubio's claim on Fauci's stance on herd immunity levels. Last week, The New York Times reported that Fauci acknowledged he was "slowly but deliberately" raising his estimates for the level of vaccination needed to reach herd immunity.

According to the article, Fauci said, "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." But even in his interview with the New York Times, Fauci shied away from a definitive number and reiterated that there's a range of possibilities.

Fauci clarified his stance in an interview with CNN's Dana Bash on State of the Union Sunday that aired more than an hour before Rubio tweeted.

When asked why he wasn't straightforward to begin with about the higher level of vaccinated population necessary to achieve herd immunity, Fauci pushed back on the idea that he had used certain data points to distort people's perception. "I don't think it can be interpreted as being straight or not," he said, adding that "these are pure estimates," and later that "nobody really knows for sure."

Fauci explained that he was not primarily basing his recommendation on polling about public perception of the vaccine but that his higher estimates were influenced by the highly transmissible measles, which needs at least 90% of the population vaccinated to maintain herd immunity.

"That's not a big leap to go from 75 to 85. It was based on calculations and pure extrapolations from measles," Fauci said. He noted the range for the coronavirus is likely less than 90% because the coronavirus is less transmissible than measles.

On masks

Fauci told CNN's Chief Medical Correspondent Dr. Sanjay Gupta during a CITZEN by CNN Conference that his evolving advice about masks is a "classic example" of how guidance can change as additional scientific evidence emerges. The pandemic, he said, is an "evolving situation."

In March, both the World Health Organization and the CDC said face masks should be reserved for those who are sick or caring for the sick, but later reversed their guidance after doctors learned more about how the coronavirus spreads.

Fauci explained that in the spring, "we were not aware that 40 to 45% of people were asymptomatic, nor were we aware that a substantial proportion of people who get infected get infected from people who are without symptoms." Once that became clear from the data, Fauci said, "that makes it overwhelmingly important for everyone to wear a mask."