Rubella, also known as German measles or "three-day measles," is a contagious viral infection that brings on a rash as well as other symptoms. But many children have such mild symptoms that they're unaware of being infected. It's milder than measles and doesn't last as long.
Rubella is a significant health risk for pregnant women. If a pregnant woman is infected with rubella, especially in the first trimester (1 to 3 months), she may miscarry or the fetus may suffer severe birth defects.
After a bout with rubella, a person has lifelong immunity. The disease used to be common, with epidemics sweeping across North America every 6 to 9 years. Major epidemics occurred at a frequency of every 30 years, with the last one recorded in 1964, affecting over 12 million people in the US.
The virus was first isolated in the laboratory in 1962 and a vaccine was made available in 1969. Since then, the measles-mumps-rubella (MMR) vaccine has cut the frequency of the disease dramatically in countries that include the vaccine in their immunization programs.