Immunity after a single infection varies depending on the disease. For many viruses, such as influenza or COVID-19, immunity may be temporary or strain-specific, meaning a person could get infected again if exposed to a different variant. Recurrent cases are relatively uncommon for infections that produce strong, long-lasting immunity (like measles), but they are more frequent for viruses that mutate rapidly, leading to new strains that can evade previous immunity. Overall, reinfections are possible, especially when the pathogen evolves or the immune response wanes over time.