The human papillomavirus vaccine, sold under the brand name Gardasil, may be effective in preventing the vulval and vaginal lesions that cause cancer, according to a new study.

Clinical trials involving more than 18,000 women ages 16-26 in 24 countries across the United States, Europe and Asia showed that the vaccine prevented vulval and vaginal cancers in 71 percent of women previously exposed to HPV and in 100 percent of women who had not been exposed to the virus prior to using the vaccine.

The study was conducted by Professor Jorma Paavonen, of the Department of Obstetric and Gynecology at the University Central Hospital in Helsinki, Finland, and his colleagues. It was published in this week’s edition of The Lancet.

The study’s authors say there has been a “striking” increase of high-grade vulval pre-cancer lesions, as well as vulval cancer in the past 30 years.

“This trend is worrying because these cancers are not amenable to a screening (program),” the authors wrote in the study. “Whereas, previously vulval cancer was seen almost exclusively in older women, recent studies have shown that 20 percent of these cancers now occur in women under 50 years (of age).”

The authors said vulval and vaginal cancers are dangerous because they are often not recognized. And treatment of these cancers “can be mutilating” and cause patients “anxiety, depression, sexual dysfunction and poor self-image.”

For maximum results, girls should be vaccinated before they become sexually active. The vaccines effectiveness in preventing vulval and vaginal cancers in women that are already sexually active is expected to be lower due to the prevalence of HPV, the authors said.