Some never infected. How and why?

Researchers want to study people who are potentially immune

When her partner tested positive for the coronavirus two days before Christmas, Michelle Green worried she, too, would become ill. She was two months pregnant with their second child. He was a bartender at the time, and some of his co-workers were infected with the virus.

“I told him to get in the guest bedroom and don’t leave,” said Green, a 40-year-old project manager at a retail technology start-up in the District of Columbia. The couple and their toddler postponed their Christmas celebration. Somehow, Green never tested positive.

Scientists around the world are investigating how a dwindling number of people such as Green have managed to dodge the coronavirus for more than two years, even after the highly transmissible omicron variant drove a record-shattering surge in cases this winter.

A majority of Americans have contracted the novel coronavirus since it began to spread in the United States in early 2020, according to the Centers for Disease Control and Prevention.

Experts hope that studying people who have avoided infection may offer clues — perhaps hidden in their genes — that could prevent others from being infected or more effectively treat those who contract the virus.

“What we are looking for is potentially very rare genetic variants with a very big impact on the individual,” said András Spaan, a clinical microbiologist and fellow at the Rockefeller University in New York who is spearheading a search for genetic material responsible for coronavirus resistance.

Screening for study

Spaan said the international study already has enrolled 700 participants and is screening more than 5,000 people who have come forward as potentially immune to coronavirus infection.

One of the study participants is 49-year-old Bevin Strickland, a nurse anesthetist from Highpoint, N.C., who volunteered in a Queens hospital for six weeks beginning April 2020, just as that pocket of New York City became the epicenter of the pandemic.

“By the second day, I didn’t even care about getting COVID because the patients were just heartbreaking,” said Strickland, who often worked without a mask to better connect with confused patients.

Most of the worst cases were seniors who had been living in nursing homes. Some didn’t speak English. Many were disoriented from not getting enough oxygen as they struggled to breathe.

“I was taking off my mask all the time just so they could see my face,” Strickland said. “That would help us get (an oxygen) mask on them and help us treat them.”

Strickland was tested weekly for coronavirus. She never tested positive. When her volunteer stint ended, she also took an antibody test that showed no evidence of a prior infection.

Natural immunity?

Neither of Strickland’s parents have had the virus, nor has her twin sister, who works as a primary care doctor. When both she and one of her twin sons managed to evade illness even after her other son endured a COVID infection inside their 1,200-squarefoot house, Strickland began to suspect she may have a natural immunity to the virus. So she sought out the scientific study looking at the genetic makeup of people like her who never contracted the coronavirus despite repeated exposures.

“I really do feel hopeful that they’re going to see some kind of similarity, some kind of gene in our DNA,” Strickland said.

Studying the genes and other biological traits of people who never catch the coronavirus could shed light on how the virus develops, or how it infects the human body and makes people sick, said Jennifer Nuzzo, a professor of epidemiology at the Brown University School of Public Health. The findings could lead to better drugs and more targeted public health advice.

Scientists don’t know why some people might be impervious to the coronavirus, but Nuzzo said one hypothesis could be that some individuals have fewer receptors in their noses, throats and lungs for the virus to bind to. Other possible explanations could be prior exposure to a related virus or simply being born with an immune system better suited to fighting SARS-CoV-2.

But finding individuals who have truly never had a coronavirus infection — not just those who had an asymptomatic infection or less severe case of COVID-19 and did not know they had contracted the virus — is tricky.

“Those people should be exceedingly rare in the United States at this point,” said Christopher Murray, director of the Institute for Health Metrics and Evaluation at the University of Washington and who helps develop models that estimate how far the virus has spread.

Up to 76% could have been infected

HME models suggest that the number of people who have had the coronavirus in the United States may be even higher than recent CDC estimates based on blood tests, Murray said. The CDC said nearly 6 in 10 Americans have had the virus at least once; IHME estimates that total is closer to 76% of U.S. residents.

Antibody tests can rule out people who have an immune response to the virus, but some of those tests cannot distinguish between people who have antibodies because of vaccines and those who have had the coronavirus, Murray said. The accuracy of many antibody tests wanes over time, so they may not identify someone who had been infected months ago, he added.