This combination vaccine protects children against Measles, Mumps and Rubella. The first dose of the MMR vaccine is given between 12 to 15 months, the second between four to six years old. These childhood infections are quite contagious and once were common among children in the US. These illnesses are still common in developing countries, and can be to the United States. Therefore, even with few cases in the U.S., it is important to maintain high levels of immunity among U.S. children by continuing to vaccinate them. Current practice is to screen all pregnant women in this country for immunity to rubella, as infection in a fetus can be devastating.