The MMR vaccine is a combined vaccine that protects against three serious diseases: measles, mumps, and rubella. It is a live virus vaccine that causes a harmless infection in the vaccinated person with very few, if any, symptoms before they are eliminated from the body. The person’s immune system fights the infection caused by these weakened viruses, and immunity develops. Children should get two doses of MMR vaccine, starting with the first dose at 12-13 months and the second dose at 3 years and 4 months. Adults who are not already immune to measles, mumps, and rubella may also need 1 or 2 doses of MMR vaccine. The vaccine is very effective at protecting people against these diseases and preventing the complications caused by them. The MMR vaccine does not contain mercury (thiomersal) . There is no link between the MMR vaccine and autism.