How does the MMR vaccine work?

The MMR Vaccine contains tiny doses of living but inactivated viruses that cause measles, mumps and rubella. Once these viruses are injected into the body, the immune system will develop certain antibodies against these three diseases shortly following vaccination. Because your body has memory cells it now knows how to defeat these diseases when they enter the body again, and it will know which certain antibodies it needs to produce; these antibodies in your body will give a lifelong protection against these diseases.