Sen. Rand Paul, R-Ky., and Dr. Anthony Fauci, the nation's top infectious disease specialist, sparred Wednesday over the country's efforts to mitigate the spread of Covid-19 and when "herd immunity" from the virus is reached.
The unusually testy exchange occurred during Fauci's testimony in front of the Senate Committee on Health, Education, Labor and Pensions.
During his questioning, Paul, who was a practicing ophthalmologist before he was a senator, said that some states in the Northeast, specifically New York, allowed the coronavirus to spread unchecked before locking down, leading to widespread cases and death.
It is true that New York leads the country in Covid-19 deaths: Nearly 34,00 people have died of the virus in the state, the vast majority in the spring, according to an NBC News database.
"New York had the highest death rate in the world," Paul said. "How can we possibly be jumping up and down and saying, 'Oh, Governor Cuomo did a great job!'" he added, referring to Andrew Cuomo, a Democrat.
"No, you misconstrued that, senator. And you've done that repetitively," Fauci responded, adding that New York was hit badly as the virus was spreading silently before cases of severe disease erupted. He also acknowledged the state "made mistakes" but did not elaborate.
New York "probably should have closed a week or two earlier than they did," Dr. Ashish Jha, dean of the school of public health at Brown University, told NBC News in an interview. But, he added, "if anybody can tell you that they knew in February that New York was getting hit hard, and should have done something different, they're smarter than anybody else. None of us knew it was going to be that bad."
Fauci, director the National Institute of Allergy and Infectious Diseases, noted during the exchange with Paul that New York has been able to bring down its test positivity rate to 1 percent or less because the state adhered to guidelines such as wearing masks, social distancing outdoors, avoiding crowds and washing hands.
Paul cut off Fauci, dismissing those mitigation efforts. He implied instead that New Yorkers have "developed enough community immunity" to beat the pandemic.
"I challenge that," Fauci said. "You were not listening to what the director of the CDC said, that in New York, it's about 22 percent. If you believe 22 percent is herd immunity, I believe you're alone in that."
Herd immunity occurs when enough people become immune to a contagious disease, making further spread unlikely. Those trained in infectious disease say at least 60 percent of a population needs to have been exposed to a virus to reach herd immunity.
But Paul referred to research suggesting people have "pre-existing, cross-reactive immunity to coronavirus," which "may explain why we have so many people that have very little symptoms or are asymptomatic."
Because most of us have been exposed to other coronaviruses, such as those that cause the common cold, our immune systems may already be trained to recognize SARS-CoV-2, the coronavirus that causes Covid-19.
There has been some research to back the theory cited by Paul, including one study that found immune cells called T cells could indeed account for the wide range of severity of Covid-19 symptoms.
However, Fauci responded by citing a recent study that found no evidence of pre-existing immunity from other coronaviruses.
Fauci was referring to a study published last week in The Journal of Infectious Diseases, a NIAID spokesperson told NBC News. That study found that while exposure to previous common coronaviruses had an impact on infection with other common coronaviruses, it had no effect on SARS-CoV-2 infection.
Other experts agreed. "There's absolutely no evidence that having a cold from a coronavirus in the past does anything to protect us," Dr. Michael Saag, associate dean for global health at the University of Alabama at Birmingham, told NBC News. "If it did, we wouldn't have the epidemic we're having right now."
Even if there were a degree of cross-reactivity, it would not necessarily mean it would be strong enough to fight key components of this particular coronavirus, experts said. In this case, it's the spike protein on the surface of the virus that acts as the key that unlocks the body's cells to infect them.
"Coronavirus immune responses go away after about four to six months," Saag said. "That's why we get the common cold over and over again."
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Paul, who was the first senator to test positive for the coronavirus, in March, also compared the responses to Covid-19 in New York and New Jersey to that of Sweden.
Swedes went on with life as usual, for the most part, during the pandemic, without closing bars or restaurants. The country, which Paul lauded as having a "softer touch" on lockdowns, has logged just under 6,000 Covid-19 deaths.
Fauci countered, saying that it is not appropriate to compare Sweden's death rate with the U.S.
"Compare Sweden's death rate to other comparable Scandinavian countries," Fauci said. "It's worse."
Indeed, Switzerland has reported about 2,000 Covid-19 deaths, while Denmark, Finland and Norway have had about 1,200 such deaths combined, according to the Johns Hopkins Coronavirus Resource Center.
"The virus is very simple to understand," Saag said. "It will infect anyone when given the opportunity."