Reinfection refers to the phenomenon of an individual becoming infected with a particular pathogen more than once after having recovered from a previous infection. This can happen with various infectious diseases, including viral infections like COVID-19 and bacterial infections like tuberculosis. Reinfection can occur due to a weakened immune response, the presence of new strains of the pathogen, or a combination of factors. Studying reinfection is important for understanding the natural history of diseases, improving preventive measures, and developing more effective treatments.