Men who have sex with men (“MSM”) have long been considered one of the populations at greatest risk for HIV infection; yet, few studies reporting on condom effectiveness in preventing transmission among this community have been conducted. Johnson et al. performed a meta-analysis of existing data to estimate condom efficacy for unprotected receptive anal sex between serodiscordant couples by measuring risk for people who sometimes or never use condoms and people who always use condoms. The analysis showed that the risk of HIV infection rose by 83% for sex acts where partners rarely or did not use condoms, while risk of HIV transmission rose by only 7% for partners who always use condoms. The final estimate of condom effectiveness by Johnson et al. is 91% -- higher than past estimates using the same type of meta-analysis. This new estimate is fundamental to a more accurate understanding of the effectiveness of condom usage in preventing HIV acquisition.
Until now, two major papers, Scott et. al. (2014) and Smith et al. (2015) produced estimates which together established accepted understandings of condom efficacy and HIV transmission among MSM. Scott et. al estimated condom effectiveness to be 89% while Smith et al. estimated condom effectiveness to be 72%. Johnson et al. uses the same data sets as Scott et. al. and Smith et al., but uses a different unit of exposure by which to measure risk: Johnson et al. quantifies exposure per-partner while both Scott et al. quantified exposure per-act and Smith et al. used combined methods of per-act and per-person-per-year. Not only is this new estimate critical to our understanding of the effectiveness of condom usage, but it also underscores the need for continuing community-level studies assessing risk and prevention methods.