Very few people—about five out of 100—who get two doses of measles vaccine will still get measles if exposed to the virus. It could be that their immune systems did not respond as well as they should have to the vaccine.

The good news is, fully vaccinated people who get measles seem more likely to have a milder illness and fully vaccinated people seem less likely to spread the disease to other people, including people who cannot get vaccinated because they are too young or have weakened immune systems.