The MMR vaccine is a vaccine given before children enter school. It helps to prevent measles, mumps, and rubella, three potentially serious illnesses. The MMR is given in two doses, the first around 1 year of age and another before entering kindergarten. Adults who have not gotten the vaccine should do so. In some cases the MMR is combined with the chickenpox vaccine and is called an MMRV vaccine. Follow the links below to find WebMD's comprehensive coverage about how the MMR vaccine works, side effects, benefits and risks, and much more.