The U.S. Centers for Disease Control and Prevention said Thursday that the number of teens ages 13 to 17 who are receiving the human papillomavirus (HPV) vaccine remains “unacceptably low.” A phone survey conducted by the CDC showed only a small rise in HPV vaccination levels, which is “bad news for cancer prevention,” as the director for the CDC’s National Center for Immunization and Respiratory Diseases said. HPV is the most common sexually transmitted infection and has been linked to several types of cancer, including cervical. The CDC has recommended that girls and boys be vaccinated at age 11 or 12, so they develop immunity before becoming sexually active.