An international clinical trial indicates that a vaccine against two types of high-risk Human Papillomavirus (HPV-16 and HPV-18), which cause an estimated 70 percent of cervical cancer cases, can significantly decrease the incidence and mortality rates for this disease worldwide, according to an article in the November 13th issue of Lancet.

Currently, an estimated 280,000 women die from cervical cancer each year, most of them in the developing world. Of the 500,000 cases of cervical cancer diagnosed annually, 70 percent are attributed to infection from HPV-16 and 18. The five-year prevalence of cervical cancer worldwide is 1.4 million.

In the blinded, randomized trial of 1,113 women from throughout the U.S., Canada, and Brazil, participants received three doses of the experimental vaccine or a placebo over six months. At 27 months of follow-up, the vaccine showed an extremely high rate of efficacy, according to the authors. In those women who completed the protocol - receiving all three shots and participating in all scheduled testing and follow-up - the vaccine was 100 percent effective against persistent HPV16/18 infection.

Significantly, the efficacy was only slightly reduced for women who did not fully comply with the protocol - receiving only one or two of the three shots or not completing all scheduled follow-up appointments. In that group, the vaccine proved 95 percent effective against persistent HPV infection and 93 percent effective against cytologic abnormalities associated with HPV16/18, along with complete protection from cervical tissue changes due to HPV16/18.

Harper is internationally recognized for her pioneering work on HPV. She called the results of the study "extremely exciting and encouraging. We believe this shows enormous potential to eradicate the great majority of cervical cancers worldwide."

Harper noted that while other vaccines against HPV are currently being tested, this trial is notable because it is the first to target two viruses with one vaccine. "Our trial results showed a high degree of safety, with no adverse effects to the participants, and highly significant and complete protection against persistent infection. This has enormous implications for women worldwide, and for our health system, which annually spends billions of dollars on cervical screening programs."

Recruitment for a larger, Phase III trial of the vaccine is now underway, Harper said. "We hope these results will encourage women to sign up for this trial."