All HIV-positive gay men should receive Gardasil, the vaccine that prevents cancerous human papillomavirus (HPV) types 16 and 18, say researchers who presented data at July’s International AIDS Society Conference in Sydney, Australia. The prevalence of these strains in a cohort study hints that mass immunizations may reduce the likelihood of anal cancer in this high-risk population, according to AIDSmap.

Of the 70 HIV-positive California and Illinois patients who had anal Pap smears, 33 were found to be positive for HPV infection—41 percent of whom had HPV types 16 and/or 18. To the Veterans Administration investigators conducting the study, this high rate of cancer-causing infection signals a “strong rationale” for a large-scale vaccination program.

Gardasil, which is also effective against HPV types 6 and 11—non-cancerous strains that can cause genital warts—is only approved for females between 9 and 29 years of age. A large clinical trial is currently exploring the vaccine’s safety and effectiveness in a study of men.