LAUSR

www.thelancet.com Vol 392 December 1, 2018 2335 The HIV/AIDS community is paying increasing attention to the estimated 1·8 million (uncertainty bounds 1·3 million to 2·4 million) people younger than 15 years living with HIV globally, as was evident by the focus on adolescents at the XXII International AIDS Conference in July, 2018. This attention is welcome, and it is crucial to curtailing the HIV epidemic. But while age disaggregation can help elucidate the spread and impacts of the HIV epidemic, it is not enough. A gender lens is also needed. Spectrum, the analytical model used by UNAIDS to estimate HIV prevalence regionally and globally, assumes that HIV is transmitted vertically, through perinatal transmission, to girls and boys at roughly the same rate. But by the time they become adolescents, there is a shift. UNAIDS data indicate that 61% of adolescents aged 15–19 years living with HIV are girls, and that two-thirds (66%) of new HIV among adolescents in this age group occur in girls. The proportion of new HIV in girls suggests that horizontal transmission, particularly through sex, is a greater factor for adolescent girls than for boys, which has implications for HIV prevention, treatment, and care. However, few studies and interventions disaggregate the modes of transmission when addressing the needs of adolescents for prevention and treatment of HIV. There are limited population-level data for HIV transmission in adolescents through injecting drug use, although, based on existing data, we assume that at a global level such transmission is likely to be minimal. Sexual transmission requires further investigation. The widely used Multiple Indicator Cluster Surveys and Demographic and Health Surveys do not collect data on sexual behaviours for adolescents aged 10–14 years, although as Santelli and colleagues argue, there are ways to conduct minimal risk research with this population. Stemming HIV in adolescents: gender and modes of transmission control, nor will focusing efforts on one target population or one gender. We must continue to expand programmes to protect adolescent girls and young women from HIV infection, but we must not give up on reaching men. Success in controlling the HIV epidemic depends on it.