The number of people who have never been infected by the coronavirus is shrinking—and even people who believe they've never contracted the virus may well have had asymptomatic infections, Julie Wernau writes for the Wall Street Journal.

The 'never Covid' cohort is shrinking

According to epidemiologists, most people worldwide have been infected by the coronavirus at least once at this point in the pandemic. For example, CDC data estimates that roughly 58% of the U.S. population contracted Covid-19 through February, and daily reported infection rates in the United States continue to be high at over 100,000 cases.

But some people have never gotten sick or tested positive for Covid-19 and may consider themselves part of the "never Covid" cohort.

"It's probably a combination or being careful, maybe being blessed with a good immune system," said Charley Ding, an anesthesiologist in Illinois who was able to avoid contracting Covid-19 even when many of his colleagues did. "But also just luck."

However, according to Susan Kline, a professor of medicine at University of Minnesota Medical School, many of the people who believe they have never been infected have had asymptomatic infections and not realized it. According to a meta-analysis published in the Journal of the American Medical Association, around 40% of confirmed Covid-19 cases are asymptomatic.

Some antibody tests can determine whether someone has ever been infected by identifying nucleocapsid antibodies, which are different from the spike protein antibodies generated by Covid-19 vaccines. However, only 90% of people who get Covid-19 will generate detectable antibodies, making it harder to identify the remaining 10% with prior infections.

"There are probably a fair number of people out there who did get Covid and didn't make antibodies," said Sheldon Campbell, a pathologist and lab medicine doctor at Yale Medicine.

Steve Jameson, from University of Minnesota Medical School, said people who don't know if they've been infected should continue to be careful. "There are plenty of people who've had the vaccines or even had Covid and then have gotten Covid again," he said. "It's not as if it makes you immortal."

Are there factors that could protect people from Covid-19?

Currently, researchers are studying potential factors that could prevent the coronavirus from infecting some people or affect how someone responds to the virus.

"There are superspreaders who get infected and have no symptoms and there are others who have risk factors that make them much more susceptible," said Steven Lipkin, a clinical geneticist at Weill Cornell Medicine.

According to Wernau, some research suggests that exposure to other pathogens may generate an immune response against the coronavirus. For example, a recent study published in Science Immunology found that some people had T-cells in their guts and on their skin that appeared to help them combat the coronavirus.

Similarly, a small study published in Nature Communications suggests that immunity against common cold coronaviruses may provide some protection against SARS-CoV-2 infection. "Some people come with a bit of a head start," Jameson said.

Other research has examined the genomes of Covid-19 patients for genetic variations or mutations that could impact their immune response or their susceptibility to the coronavirus.

According to Gigi Gronvall, an immunologist and senior scholar the Johns Hopkins Center for Health Security, a genetic predisposition against infection "is seen in other diseases where people have one or multiple factors that interfere with virus binding to cells or being transported within." (Wernau, Wall Street Journal, 7/25)