The disease is caused by a virus that is spread through the air or by close contact. It can also be transmitted to a fetus by a mother with an active infection, causing severe disease in the fetus. In children and adults, rubella is usually mild and may even go unnoticed.

Children generally have few symptoms, but adults may experience fever, headache, malaise, and a runny nose before the rash appears. A person can transmit the disease from 1 week before the onset of the rash, until 1-2 weeks after the rash disappears. The disease is less contagious than rubeola (measles). Lifelong immunity to the disease follows infection, and there is a safe and effective vaccine to prevent rubella.

Rubella is most serious because of its ability to produce defects in a developing fetus if the mother is infected during early pregnancy. Congenital rubella syndrome occurs in 25% or more of infants born to women who acquired rubella during the first trimester of pregnancy.

Defects are rare if the infection occurs after the 20th week of pregnancy. One or more defects may occur in an infected fetus and include deafness, cataracts, microcephaly, mental retardation, congenital heart defects, and other problems. A miscarriage or stillbirth may occur.

Risk factors include lack of immunization and exposure to an active case of rubella.