MODEL RELEASED. MMR vaccination. Nurse about to inject the MMR vaccine into the leg of a 16-month- old baby girl being held by her mother. MMR is a combined vaccine to protect infants from 3 viral diseases: measles, mumps and rubella. The first injection is given in the infant's second year, with a booster at 4-6 years of age. The vaccine consists of weakened samples of the three viruses, causing a weakened response from the body's immune system, which prepares defences against future infection. Measles is a potentially fatal disease. Vaccines are given to babies and young children as part of a childhood vaccination schedule. Combined vaccines speed up this process.