Most people likely know someone who somehow avoided catching COVID-19 despite living in the same crowds and routines as everyone else. Is there a scientific reason why some individuals appear resistant to infection when the virus seems everywhere? Or is it mainly luck?
Estimates suggest that the actual number of people who have been infected with SARS-CoV-2 is higher than the number of lab-confirmed cases. Across studies, the share of infections that were asymptomatic varies, but consensus among experts is that asymptomatic infections are common and part of the broader picture of transmission.
Even among those who never realized they had COVID-19, there may be a subset of people who have never become infected in the first place. Why certain individuals seem immune to COVID-19 remains a persistent question. As with many scientific topics, there is no single, simple explanation yet.
The most straightforward idea is that these individuals simply were not exposed to the virus. This could be true for people who wore protective gear or who avoided high-risk environments during the height of the pandemic.
Yet given the widespread presence of the virus in communities, especially with highly contagious omicron variants, it is unlikely that someone who goes to work, school, or stores would never be near an infected person. Even among healthcare workers, there are people who avoid a positive test result.
Multiple studies show that vaccines do more than protect against serious illness; they can also reduce the chance of transmitting the virus by roughly half. Vaccination can help some people steer clear of infection, though it is important to note that many studies were conducted before the omicron era. Data on how vaccines affect omicron transmission remain limited and evolving.
One idea is that some people, after exposure, do not become infected even when the virus reaches the respiratory tract. This may relate to the virus lacking certain receptors needed to enter cells, or to other immune factors at work that block initial infection.
Researchers have found that how the immune system responds to SARS-CoV-2 largely influences illness severity. In some individuals, a rapid and strong immune response can greatly limit viral replication, leading to milder outcomes. The strength of this immune response is shaped by a mix of age, genetics, and overall health. A healthy lifestyle can support defense against pathogens; for instance, vitamin D status and adequate sleep play roles in immune readiness. In some severe cases, genetic factors have been linked to vulnerability, and ongoing work suggests genetics might also contribute to resistance in other people, though the exact mechanisms are still under investigation.
There is also the possibility that prior exposure to other coronaviruses could prime the immune system to recognize SARS-CoV-2, offering a head start in mounting a response. This concept of cross immunity could help some people respond more quickly to the new virus. Another line of inquiry is how long any such immune protection lasts. Seasonal coronaviruses circulating before 2020 could re-infect the same individuals after about a year, underscoring the uncertain duration of any cross-protective effects.
If someone has managed to avoid COVID-19 so far, it could reflect natural immune defenses, lucky exposure patterns, or a combination of factors. Whatever the case, continuing to take sensible precautions remains wise, especially given the limited understanding of how the virus may evolve and the potential for new variants to emerge. This cautious approach helps protect individuals and communities while researchers refine knowledge on immunity, exposure, and transmission.