In this study, researchers quantified data to study the safety and efficacy of prophylactic human papillomavirus (HPV) immunization for males who have had sex with males (MSM). They noted a decline in the incidence of anogenital HPV infections with targeted vaccination to about 30% after 40 years, with a range of 10% to 50%, based on the recruitment of MSM into targeted campaigns and on the assumed mode of vaccine protection. They noted a further increase to 75% after 60 years when targeted vaccination was combined with sex-neutral vaccination in preadolescence, conferring uptake of 40% among 12-year-old boys and 85% effectiveness against future HPV16 infections in MSM. Overall, findings supported targeted vaccination to protect adult MSM, at least temporarily, at high risk for anal cancer.