Rubella is a contagious disease caused by a virus. Most people who get rubella usually have a mild illness, with symptoms that can include a low-grade fever, sore throat, and a rash that starts on the face and spreads to the rest of the body. Rubella can cause a miscarriage or serious birth defects in a developing baby if a woman is infected while she is pregnant. The best protection against rubella is MMR (measles-mumps-rubella) vaccine.