Many scenarios developed following the COVID-19 epidemic caused by SARSCoV-2 assume that the infection results in an immune response that confers immunity or reduces the severity of a possible reinfection. The presence or absence of protective immunity due to infection or vaccination will affect future transmission and disease severity. COVID-19 infection leads to the production of IgG and IgM class antibodies after a few days or weeks. However, it remains to be understood why the infection is sometimes not followed by antibody production in some subjects. IgG antibodies develop a secondary immune response, which occurs on subsequent exposures to the same antigen.