Virus Transmits much more Easily Via Anal Intercourse, Research Shows New research pinpoints a major reason why gay and bisexual men remain so vulnerable to the AIDS epidemic: When it comes to the transmission of HIV, a man who has unprotected anal intercourse is at especially high risk. In fact, if that kind of intercourse was only as risky as vaginal intercourse, researchers report, HIV cases among gay and bisexual men would shrink dramatically. It would go down even more, they added, if their rates of casual sex declined. [. . . ] According to UNAIDS, HIV is more common...