How effective is the measles (MMR) vaccine?

The MMR (measles-mumps-rubella) vaccine is highly effective. A single dose provides approximately 93% protection against measles; two doses provide approximately 97% protection. The two-dose schedule — first at 12–15 months, second at 4–6 years — is the global standard recommended by WHO and CDC and is why measles was declared eliminated from the USA in 2000. Protection from two doses is generally lifelong for the vast majority of vaccinated people. Adults born before 1957 are presumed immune from prior natural infection. Adults born in 1957 or later who haven't had measles or received two vaccine doses should get vaccinated. The 2025–2026 USA resurgence is driven entirely by communities with low two-dose MMR coverage — not by the vaccine failing, but by vaccination gaps allowing the virus to find susceptible hosts.