With the advent of the second and third waves of COVID-19, the efficacy of the vaccines might become questionable. The common cold-causing strains of coronavirus can reinfect an individual multiple times. This is due to its ability to meddle with the immune memory cells. When viral infection occurs, IgM is produced within two weeks which mobilizes against the virus and gradually disappears.
This is followed by the secretion of IgG antibodies which persist for several years. But this is contradictory to human coronavirus. Antibodies against SARS-CoV-2 fade over time leaving the individual susceptible to reinfection. It was also detected that SARS-CoV-2 infected asymptomatic individuals had low levels of antibodies when compared to symptomatic counterparts, making the symptomatic individuals more susceptible. Reinfections with the common cold are easily cured but COVID-19 reinfections are much more lethal depending upon the health status. If the immune cells against SARS-CoV-2 fade easily the concept of herd immunity will be totally ineffective.
The reason for SARS-CoV-2 reinfection is yet to be thoroughly analyzed. But with respect to previous studies carried on viruses or viral diseases, it can be hypothesized that the SARS-Cov-2 can target and kill the memory B-cells. Secondly, like the flu virus, the COVID-19 virus might have the ability to cause antigenic drift for which multiple generations of vaccines might be required. Contemplating the aforementioned possible effects of the SARS-CoV-2 on the immune system few questions must be analyzed while vaccine development- how long immunity will last, how strong is the immune response created, and the mechanism by which SARS-CoV-2 can reinfect.
Ref link: https://www.scientificamerican.com/article/what-covid-19-reinfection-means-for-vaccines/