A vaccine developed to prevent infection with human papillomaviruses (HPV), the cause of cervical cancer, was found to be ineffective for treating women with pre-existing HPV infections, according to a study published in the August 15 Journal of the American Medical Association.

The study, a community-based, randomized trial of 2,189 women in Costa Rica, was conducted by NCI's Division of Cancer Epidemiology and Genetics (DCEG) and Costa Rican investigators. The researchers found no significant difference in how quickly an HPV infection was cleared among those who received the HPV vaccine compared with the control group who received vaccinations for hepatitis A. At the 6-month follow-up visit, rates of viral clearance were 33.4 percent for women who received vaccines against HPV types 16 and 18 compared with a 31.6 percent rate among the control group. At the 12-month visit, rates of clearance in the HPV vaccine group were 48.8 percent versus 49.8 percent for the controls.

"The main finding of the study was to demonstrate that among women who are already infected, the HPV vaccine does not help accelerate the rate of viral clearance," commented Dr. Allan Hildesheim with DCEG. "Therefore, women who are infected with HPV should not take the vaccine to treat their infections or associated lesions." The study reinforces the importance of targeting HPV vaccination towards adolescent girls before they begin sexual activity "because that would maximize the benefit provided by vaccination," he added.

The study is part of a larger community-based clinical trial of 7,466 Costa Rican women. The larger study will address broad issues about the vaccine including efficacy, duration of protection, and global impact of vaccination on HPV and HPV-related disease. Among other questions, "the study will address whether vaccination is important for women who have previously been infected and have cleared the infection by themselves," said Dr. Hildesheim.