The health department of Chandigarh, India, is undertaking an initiative to vaccinate about 2,000 teenaged girls against rubella, in a move to prevent their future children from being born with birth defects caused by congenital rubella syndrome (CRS). Rubella becomes most dangerous when a pregnant woman becomes infected during the first trimester, which will likely cause fetal infection, resulting in CRS. Statistics show that about 20 percent of infants born to mothers infected with rubella during the first half of their pregnancy are affected by CRS.