Australian health officials are taking part in a three-year clinical trial of a vaccine aimed at preventing human papillomavirus infections in gay men and preventing anal cancer, the Australian Associated Press reports. HPV, which is spread by sexual contact, can cause genital and anal warts and has been linked with increased risk of developing anal cancer. HPV also has been linked with cervical cancer in women. About half of all sexually active gay men are believed to have been infected with HPV; nearly 90% of HIV-positive gay men are coinfected with HPV. The vaccine trial will include young gay men ages 18-23, according to Robert Finlayson, director of the Taylor Square Private Clinic in Darlinghurst, New South Wales. HPV is the most common sexually transmitted disease in Australia, and it is estimated to be 96% more common in gay men now than it was 20 to 30 years ago, according to Finlayson.