PROS1 and COVID-19: Reinfection referred to the reinfection of the same or different types of SARS-CoV-2 strains after the removal of the initial infection with COVID-19, due to factors such as the immune system not producing enough neutralizing antibodies after the initial infection, or the mutation of the key site of receptor-binding domain (RBD) of SARS-CoV-2 S protein and other factors.