Natural resistance against infections: focus on COVID-19.

Not all individuals exposed to a pathogen develop illness: some are naturally resistant whereas others develop an asymptomatic infection. Epidemiological studies suggest that there is similar variability in susceptibility to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infections. We propose that natural resistance is part of the disease history in some individuals exposed to this new coronavirus. Epidemiological arguments for natural resistance to SARS-CoV-2 are the lower seropositivity of children compared to adults, studies on closed environments of ships with outbreaks, and prevalence studies in some developing countries. Potential mechanisms of natural resistance include host genetic variants, viral interference, cross-protective natural antibodies, T cell immunity, and highly effective innate immune responses. Better understanding of natural resistance can help to advance preventive and therapeutic measures against infections for improved preparedness against potential future pandemics.