reinfect

Reinfect is a verb used in medical and scientific contexts to describe the act of becoming infected again with a pathogen after having recovered from a prior infection. Reinfection implies that the individual cleared the first infection and was subsequently exposed to and infected by the organism again. This term is distinct from relapse or recrudescence, where the same infection persists or reactivates rather than representing a new infectious event.

Reinfection can occur for several reasons. Immunity from the first infection may wane over time, and new exposures may involve a different strain or variant that evades prior immune protection. In some diseases, natural infection or vaccination does not confer complete or lasting immunity, increasing the possibility of reinfection. High levels of exposure, changes in pathogen genetics, or compromised immune function may also contribute.

Examples of reinfection have been documented with various pathogens. For SARS-CoV-2, genomic evidence has confirmed cases where people are infected by a different viral lineage after recovery. Reinfections also occur with influenza viruses, and in some parasitic diseases such as malaria, where partial immunity can be insufficient to prevent new infections. The concept is important for understanding population immunity, vaccine design, and public health strategies.

Diagnosing reinfection typically relies on evidence of a new infectious episode after a period of clearance, often supported by genetic sequencing demonstrating distinct strains. Recognizing reinfection helps distinguish it from relapse and informs clinical management and surveillance efforts.