(AP) -- Only about half of the teenage girls in the U.S. have rolled up their sleeves for a controversial vaccine against cervical cancer - a rate well below those for two other vaccinations aimed at adolescents.

The Centers for Disease Control and Prevention reported Thursday that 49 percent of girls had gotten at least the first dose in the three-shot vaccination series against , or HPV. The sexually-transmitted bug can cause cervical cancer and genital warts.

The reason for the low rate? Some experts think parents are uneasy with the sexual issues attached to the vaccination.

In contrast, the CDC said about two-thirds of teens have gotten shots for and tetanus, diphtheria and whooping cough.