reinfections

Reinfections refer to a new infection by a pathogen after a person has recovered from an earlier episode. Reinfection can involve the same organism with a different strain or serotype, or a closely related pathogen. It is distinct from relapse, where latent infection reactivates, and from recrudescence, where symptoms recur due to incomplete clearance of the original infection. The concept applies across many infectious diseases.

Several factors influence reinfection risk: immunity that wanes over time or is incomplete; antigenic variation in the pathogen that reduces prior immune protection; high exposure or infectious doses; and gaps in vaccination coverage. Prior infection or vaccination often reduces severity rather than fully preventing reinfection, particularly when new variants emerge.

Reinfections have been documented for a range of human pathogens. Seasonal coronaviruses and SARS-CoV-2 show reinfection despite prior immunity. Influenza viruses can reinfect due to antigenic drift. Dengue virus reinfection can occur with different serotypes, and malaria parasites may cause subsequent infections even after treatment. Tuberculosis can also recur as reinfection in high-transmission settings, though relapse from a persistent infection is possible.

Diagnosis typically relies on clinical timing, laboratory confirmation of a new infection, and, when possible, genomic comparison showing a genetically distinct strain from the first episode. Serology and timing help distinguish reinfection from persistent shedding or relapse, but objective evidence of a new infection is ideal.

Understanding reinfections informs vaccination strategies and public health measures, including booster programs and surveillance for emerging strains. It highlights that protection from previous infection is not absolute and that infection prevention remains important, especially for vulnerable populations and during outbreaks of rapidly evolving pathogens.