pre-exposure prophylaxis

Short definition from Wiktionary

Noun

1. 1
   A form of prevention, usually medication, that is taken before exposure to a pathogen, preventing development of disease after such exposure.
2. 2
   A form of prevention, usually medication, that is taken before exposure to a pathogen, preventing development of disease after such exposure: A preventative medical regimen of HIV medicines used to protect against HIV seroconversion after an exposure.