Second wave of Covid-19 is determined by immune mechanism

A second wave of new severe acute respiratory syndrome coronavirus 2 (Covid-19) cases is widely feared. In fact resurgence of cases has been clearly observed in several countries that had seen flattening of the epidemic curve. In general, relaxation of community control measures is almost always blamed for the resurgence of cases. In this letter, the author describes an immunological explanation for the double-peaked epidemic curve of new viral diseases including Covid-19. According to this hypothesis, a second wave of cases is due to the effective innate immunity in some of the population. These individuals may later develop clinical disease upon repeated exposure. This theory claims that a double-peaked pattern of new cases in a new viral epidemic is intrinsically determined by the pattern of pathogen interaction with the host. According to this hypothesis, relaxation of the community control measures is not responsible; at least in part, for resurgence of cases.