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Do some people have preexisting immunity to the coronavirus?

Mayo Clinic plasma cell researcher believes data shows we may be closer to herd immunity than many experts think

ROCHESTER, Minn — On Meet the Press on Sunday, after saying just 7 or 8% of Americans have had COVID-19, Dr. Michael Osterholm delivered this ominous message:

"This virus won't slow down even, let alone stop transmission until we get to 50 or 60%," Osterholm said.

But looking at the world's coronavirus hot spots earlier in the pandemic, Dr. Vincent Rajkumar from the Mayo Clinic points out the virus did slow down

"These hot spots have had major decreases in coronavirus cases even though they are no where near that level," Rajkumar said.

Rajkumar is one of the world's leading researchers of plasma cells, which make antibodies. He points out antibody tests were done in COVID-19 hot spots after the cases dropped, presumably showing how many people had the disease.

In Lombardi, Italy, 15-20% of the population tested positive for antibodies. In Madrid, Spain, it was 10-15%. In Sweden, where no lockdowns have ever taken place serology studies find 10 to 20% positive.

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And in New York City, where hospitals were overwhelmed in April, Rajkumar said, "The seroprevelance was only in the 20% range. Given that, you've seen the sharp drop-off of new cases in New York City. Many of the hospitals that were overflowing are almost back to normal." 

How is it possible that COVID cases steeply dropped in all these places after just 20% of the population was infected? Can it strictly be explained by human behavior, such as social distancing and masking?

"The way it's playing out in places we know, suggests that more people are immune and that we are closer to herd immunity than we think we are," Rajkumar.

Dr. Rajkumar says immune response is more complex than just an antibody count. Studies suggest people who have not been exposed to the coronavirus have T cells that fight COVID-19. It's possible the preexisting immunity comes from exposure to other coronaviruses.

Another fascinating example, Rajkumar said, is a cruise ship that left South America for Antarctica earlier in the pandemic. After a passenger tested positive, everyone was quarantined to their rooms. In 10 of those rooms, one partner tested positive and the other never contracted the disease, despite spending 20 days alone in a room with their partner.

Rajkumar believes people still need to take precautions like masks and social distancing. But if he is proven right, it offers hope for many of America's current COVID hot spots.

"I don't know what will happen, but for the sake of the country, I would hope all of these places decline very very steeply like New York did," Rajkumar said.

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