Genetics, vaccination or luck: Why some people never caught COVID-19

More than two years into the pandemic, a peculiar group persists: people who have never caught COVID-19. They exist in a shrinking minority, their continued absence of infection increasingly improbable as variants circulate and billions have been exposed. Scientists are still trying to understand why.

Myriam Domínguez, a 27-year-old from Spain living in Brussels, is one of them. She has been a close contact of infected people at least five or six times—occasions she has carefully tracked. She has flown between Madrid and Belgium without wearing a mask when it wasn't required. She returned to her office long ago and stopped masking when rules permitted. Every test has come back negative. "I find it curious," she told CNN in Spanish, "because I know people who are much more careful than me—people who avoided restaurants and friends. I've lived as normally as possible and never caught it, at least not that I know of." She follows the law as it changes, she says, but takes no extra precautions beyond what authorities mandate.

Domínguez's experience raises a question that has haunted epidemiologists since the virus emerged: What separates the infected from the untouched? According to the U.S. Centers for Disease Control and Prevention, 43.3 percent of Americans carry antibodies against SARS-CoV-2. That means more than half the population has never been infected—a gap that cannot be explained by caution alone.

Researchers have begun investigating genetic and immunological factors that might confer resistance. A study published in Nature in late 2021 outlined the search: scientists are trying to identify which genetic and immune characteristics might make someone less vulnerable to the virus. The research acknowledges that clinical responses to viral infection vary widely among individuals, and some of that variation appears rooted in human genetics. Several candidate genes have emerged as potentially involved in innate resistance to COVID-19, though the proportion of naturally resistant people remains unknown.

Dr. Elmer Huerta, an oncologist and CNN contributor, has synthesized recent research into two leading theories. The first suggests that certain people can neutralize the coronavirus because they carry antibodies and T-cell memory from past colds—cross-immunity from earlier coronavirus infections that their bodies remember and deploy. The second theory proposes that some individuals produce substances within their cells that destroy not just the invading virus but also the infected cell itself, preventing the virus from spreading. Both mechanisms, Huerta concludes, appear to be genetically determined. Some people, it seems, are protected either by the immunological echoes of old infections or by cellular defenses they were born with.

Yet none of this amounts to certainty. Scientists have found no conclusive evidence explaining why some people avoid infection despite repeated exposure. The phenomenon remains largely mysterious. Those who have escaped COVID-19 might possess natural immunity to the virus, or they might simply have been fortunate. The distinction matters less than the practical reality: even if you have avoided infection so far, you are not guaranteed to remain uninfected. Caution remains warranted against a virus that, after years of study, still holds secrets.