A large study by a team from the U.S. National Institutes of Health (NIH) finds the Cervarix human papillomavirus vaccine, which protects against cervical cancer caused by HPV, also offers strong protection against HPV-related anal cancer.

Cervarix targets HPV types 16 and 18, the strains most responsible for cervical cancer. These also "cause the bulk of anal cancers," explained study leader Dr. Aimee Kreimer of NIH's National Cancer Institute.

Researchers analyzed anal tissue specimens in a group of 4,210 healthy women ages 18-25 in Costa Rica. About half the women received Cervarix in three doses, and the other half received a placebo vaccine. After four years, the women were tested for anal and cervical HPV 16 and 18 infections.

The results indicated Cervarix prevented 62 percent of anal cancers and 77 percent of cervical cancers linked to HPV infection compared with rates in the general population. "There was strong protection with the vaccine against anal infection," said Kreimer. In participants with no likely previous HPV infection exposure, the vaccine prevented 84 percent of anal HPV, a rate comparable to that for cervical HPV infection (89 percent). Furthermore, Cervarix was found to be cross-protective against HPV types 31, 33, and 45, which also cause cancer.

"We're getting more bang for our buck than we realized with this vaccine," Kreimer said.

Approximately 5,300 new cases of anal cancer are diagnosed annually in the United States, with women comprising the majority of patients. Anal intercourse can increase the risk for anal cancers caused by HPV infections, making men who have sex with men especially vulnerable.

The study, "Efficacy of a Bivalent HPV 16/18 Vaccine Against Anal HPV 16/18 Infection Among Young Women: A Nested Analysis Within the Costa Rica Vaccine Trial," was published early online in the Lancet Oncology (2011; doi:10.1016/S1470-2045(11)70213-3).