University of Miami pediatrician, Judith L. Schaechter, M.D., gives an HPV vaccination to a 13-year-old girl in her office at the Miller School of Medicine on September 21, 2011 in Miami, Florida. The vaccine for human papillomavirus, or HPV, is given to prevent a sexually transmitted infection that can cause cancer. Recently the issue of the vaccination came up during the Republican race for president when Rep. Michele Bachmann (R-MN) called the vaccine to prevent cervical cancer 'dangerous' and said that it may cause mental retardation, but expert opinion in the medical field contradicts her claim. Texas Gov. Rick Perry, also a presidential contender, has taken heat from some within his party for presiding over a vaccination program in his home state. (Photo by Joe Raedle/Getty Images)

ATLANTA (AP) — Researchers say a vaccine for a sexually spread virus has cut infections in teen girls by half.

This is the first evidence of how well the HPV vaccine works since it came on the market seven years ago.

For girls ages 14 to 19, the study found a 56 percent reduction in the types of HPV virus targeted by the shots. Vaccination campaigns focus on girls ages 11 and 12.

Many men and women are infected with the human papillomavirus during their life. Most don’t develop symptoms and clear the infection on their own. But some infections lead to genital warts, cervical cancer and other cancers.

Results of the study by the Centers for Disease Control and Prevention were released Wednesday.

Copyright 2013 The Associated Press.