The HPV vaccine does little to speed up the reduction of HPV infections and should not be used to treat pre-existing conditions, according to a new study.

The study, published in the Aug. 15 issue of JAMA, was conducted in two provinces of Costa Rica and included 2,189 women age 18 to 25 years who were positive for HPV.

Participants randomly received either three doses of HPV 16/18 vaccine — HPV 16 and 18 are two of the most dangerous strains of the virus — or a control hepatitis A vaccine over a six-month period. Together, HPV 16 and 18 are believed to cause about 70 percent of all cervical cancers.

The study of the vaccine, sold in the U.S. under the name Gardasil, also contradicted earlier research that showed the vaccine could help treat the virus in women already infected, according to the JAMA article.

After six months, researchers found the HPV infection had cleared in 33.4 percent of those who had received the HPV vaccine compared to 31.6 percent of the participants who had received the control vaccine. At the 12-month visit, rates of clearance among participants in the control group was 48.8 percent vs. 49.8 percent for HPV group.

"Because the vaccine has no therapeutic efficacy, the greatest effect will be realized if the vaccine is administered before sexual debut, prior to exposure to HPV," said Lauri E. Markowitz, M.D., of the Centers for Disease Control and Prevention, commenting on the findings of the study.