PEOPLE WHO HAVEN’T HAD Covid-19 are now in the minority. A study found that 58% of randomly selected blood samples from adults contained antibodies indicating that they had previously been infected with the virus; among children, that rate was 75%.

And yet there are some people who believe that Covid is a hoax and avoided vaccination (lest they turn into a zombie?) that hasn’t gotten infected. There are also stories of close calls, of situations where people are sure they could have (or should have) gotten sick, but somehow dodged infection. Not all the questions are answered yet, but the question of what distinguishes the never-Covid group is a growing area of research. Here are the possibilities that scientists are considering to explain why some people haven’t contracted the virus.

They behave differently. Some people follow strictly the protocols known to reduce transmission of the virus, including wearing a mask and getting vaccinated. Others avoid large public settings and may have even been doing so before the pandemic.

The immune system, as any immunologist or allergist can tell you, is complicated. Though vaccination against Covid-19 can make symptoms more mild for some people, it can prevent others from contracting the illness altogether.

Growing evidence suggests that there may be other ways that people are protected against the virus even without specific vaccines against it. Some could have previously been infected with other coronaviruses, which may allow their immune systems to remember and fight similarly shaped viruses. Another study suggests that strong defense in the innate immune system, barriers and other processes that prevent pathogens from infecting a person’s body, may also prevent infection. An innate immune system that’s already not functioning as well due to other medical conditions or lifestyle factors such as sleep or diet may put a person at higher risk of getting sick from a pathogen. There’s no single answer here yet.

They’re genetically different. In the past, studies have found interesting associations between certain genetic variants and people’s susceptibility to communicable diseases such as HIVtuberculosis, and the flu. A study found an association between a genetic variant and lower risk of contracting Covid-19. It has been well observed that resistance embedded in genetic variation is selected in pandemics. But most experts suspect that even if they are able to identify such a variant with some certainty, it’s likely to be rare. For now, it’s best for those who haven’t gotten Covid to assume they’re as susceptible as anyone else. Whatever the reasons some people haven’t yet gotten sick, the best defense remains staying up to date with vaccinations and avoiding contact with the virus. By Manny Palomar, PhD (EV Mail June 5-11, 2023 issue)