Last Updated: 2007-05-17 18:30:04 -0400 (Reuters Health)

NEW YORK (Reuters Health) - Human papillomavirus (HPV) vaccine is highly effective in preventing high-grade, pre-cancerous lesions of the vulva and vagina among adolescent girls never exposed to the virus, according to pooled data from three large randomized clinical trials.
Among sexually active women of unknown exposure, the vaccine was still very effective, investigators report in the May 19th issue of The Lancet. They say that, with time, the vaccine could substantially reduce rates of HPV-related vulval and vaginal cancers.
The incidence of vulval carcinoma is lower than that of cervical cancer, but it has increased dramatically since the 1970s and is usually associated with HPV, Dr. Jorma Paavonen and colleagues note. Compared with cervical lesions, the rate of progression from high-grade neoplasia to invasive cancer is five times faster in lesions of the vulva and vagina.
Dr. Paavonen, from University Central Hospital in Helsinki, Finland, and associates analyzed trial data for 18,150 women from sites in the Americas, Europe, and Asia. The women, ages 16 to 26 years old, were randomly assigned to placebo or to the HPV vaccine (HPV6/11/16/18 L1 virus-like-particle vaccine). Doses were administered at day 1, month 2, and month 3.
Among women never exposed to the virus prior to completion of the vaccination regimen, the vaccine was 100% effective during mean follow-up of 3 years in preventing grade 2 and 3 vulval or vaginal intraepithelial neoplasia associated with HPV16 or HPV18.
For subjects with unknown HPV16 or HPV18 status, the vaccine reduced the incidence of HPV-associated genital neoplasia by 71%. It was 49% effective against all grade 2 or 3 neoplasia in the vagina or vulva, regardless of cause.
Dr. Paavonen's team points out that cancers of the vulva and vagina account for about 6% of all gynecological cancers, and most of those in young women are caused by HPV. Surgery is the treatment of choice, but the disease is often multifocal and adequate margins are sometimes impossible to achieve. Prophylactic treatment to prevent such cancers would save women from "mutilating" surgery, for a disease with a high recurrence rate.
The vaccine would be most effective in girls in their early adolescence before becoming sexually active, the investigators indicate. Their analysis shows that the effect of a program to vaccinate the general population of sexually experienced young women would be low at first, because of prevalent HPV infection, but would then increase as the vaccine prevented new infections.
"This intervention could greatly reduce the morbidity, mortality and health-care costs associated with these diseases," the authors conclude.