Wiktionary
post-exposure prophylaxis
n. (context medicine English) protective medical treatment after exposure to a probable source of infection, especially HIV.
Wikipedia
Post-exposure prophylaxis
Post-exposure prophylaxis, also known as post-exposure prevention (PEP), is any preventive medical treatment started immediately after exposure to a pathogen (such as a disease-causing virus), in order to prevent infection by the pathogen and the development of disease.