The MMR vaccine is a combination vaccine that protects against three contagious diseases: measles, mumps, and rubella. It is typically administered to children in two doses, the first around 12-15 months of age and the second between 4-6 years. The vaccine helps prevent outbreaks and serious complications associated with these diseases. The measles virus can cause severe respiratory issues and complications like pneumonia, while mumps can lead to swelling of the salivary glands and potential infertility in males. Rubella, also known as German measles, can cause serious birth defects if contracted during pregnancy. The MMR vaccine is an essential part of childhood immunization programs worldwide.