How does rabies post-exposure prophylaxis (PEP) differ from getting vaccinated before an exposure (PrEP)?

Treatment after an exposure (PEP) in a previously unvaccinated person requires receiving a dose of human rabies immune globulin (HRIG) and four (or five if the person’s immune system is suppressed) doses of vaccine. Pre-exposure prophylaxis (PrEP) requires only two doses of vaccine and no immune globulin. If a person who is up to date with the recommended PrEP schedule is exposed to rabies, the person’s PEP treatment is completed with two doses of vaccine (on day 0 and day 3).