If immune to measles, you are at low risk of “catching” measles, even if exposed, and will not need to quarantine after an exposure.
If not immune to measles or have an unknown immunization status, you are considered to have a high risk of catching measles. In a room of 10 non-immune people, measles will infect 9 people. You should quarantine for 21 days after your last exposure. This includes not going shopping, to work, to school, to religious services, or being with others outside of the immediate household for the full 21 days after you were exposed.
If immune globulin (IG) is given, the quarantine period is 28 days. IG provides passive antibodies that can help prevent or lessen measles, but it also delays the incubation period because it slows down how quickly the virus can multiply in the body. This means if someone is going to get sick, it might take longer for symptoms to appear — up to 28 days after exposure.