70% of new HIV cases are among homosexual and bisexual men [1]. If we assume that the incidence of homosexuals and bisexuals among men is 5%, that means that ho

70% of new HIV cases are among homosexual and bisexual men [1]. If we assume that the incidence of homosexuals and bisexuals among men is 5%, that means that homosexuals and bisexuals are 14x more likely to get infected with HIV than the general population, or 44x more likely than a non-homosexual male [2]. While 44x is certainly not "exclusive to", I think it qualifies as "mainly a problem for". And, it should go without saying, but let's hope this vaccine pans out! [1] https://www.cdc.gov/hiv/group/msm/msm-content/incidence.html https://www.cdc.gov/hiv/group/msm/msm-content/incidence.html [2] 14x is compared to the general population 5% of which is comprised by gay and bisexual men. If 70% of HIV positive people belong to a 5% group, and 30% belong to the 95% group, that's (70%/5%)/(30%/95%) = 44x is the relative risk of contracting HIV if you belong to the gay/bisexual group than if you don't belong