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Adult MSM PrEP Use May Help Lower HIV Prevalence in Adolescents

JUN 11, 2019 | EINAV KEET
A new study has modeled the use of pre-exposure prophylaxis (PrEP) drugs in both adult and adolescent men who sleep have sex with men (MSM), finding that PrEP use among adults helps to lower their HIV incidence, as well as HIV incidence among adolescents.

The study, published in PLOS ONE, notes that intergenerational sex has been found to be a key risk factor for HIV acquisition in young MSM, including adolescent sexual minority males (ASMM). Modeling studies for PrEP use among adult MSM and ASMM have typically been separate, but investigators on the study note that such modeling neglects to examine the interactions between different age groups, thus missing some of the impacts of PrEP. Although a large proportion of ASMM has not yet become sexually active, the research team notes that the group can benefit from sexual health education and promotion services, including PrEP programs. 

The current generation of ASMM is the first to come of age with PrEP as a viable option for HIV prevention from the start, although adults continue to be the targets of PrEP programs, study author Deven T. Hamilton, MPH, PhD, said in a recent interview with Contagion®.

“Adolescents are not the main focus of PrEP intervention efforts because they represent only a small fraction of new infections and this is not likely to change soon,” explained Hamilton. “I expect that the main focus of HIV prevention efforts, including PrEP programs, will continue to be on populations with higher incidence, but prevention among adolescents will be an important piece of a comprehensive approach to HIV prevention.”

Combining 2 models of HIV transmission among adults and adolescent MSM, the study team simulated an HIV epidemic among MSM aged 13 to 39 years without PrEP, with PrEP for adult MSM aged 19 to 39, and with the addition of PrEP for adolescents aged 16 to 18 years to compare the impact in terms of the percent of incident HIV infections averted along with changes in prevalence. ASMM aged 16 to 18 years were eligible for PrEP. The investigators set 6.7% of relationships reported by young adult MSM aged 19 to 25 to be with ASMM under the age of 19 while excluding contact between ASMM and MSM older than 25 years.

In the modeling, investigators found that HIV prevalence among MSM declined over 10 years from a baseline of 23.2% in the sexually active population to 17% with the inclusion of adult PrEP use at 40% coverage among eligible adult MSM. Over 40 years, adult PrEP use reduced overall HIV prevalence to 7.4%. In addition, HIV prevalence among 18-year-old ASMM not receiving PrEP dropped from 6% to 4.3% over 10 years, falling to 3.8% over 40 years.

Young people in age-discordant relationships are more likely to engage in higher-risk sexual behavior, investigators reported. “Increasing PrEP use among young adults may complement existing risk-reduction strategies for youth in age-discordant relationships by reducing the environmental conditions—high partner HIV prevalence—from which their risk accrues,” the research team concluded.

“Our work shows that the continued expansion of PrEP for adults in conjunction with PrEP programs focused specifically on ASMM can reduce the prevalence of HIV by a third among ASMM in just 10 years and by 75% over 40 years without any additional changes in treatment or prevention, bringing us much closer to the goal of an AIDS-free generation.”

The investigators note that their model only included HIV, and that PrEP use could lead to higher incidence of other sexually transmitted infections due to behavioral risk compensation. “HIV is only 1 of several STI that contribute to significant morbidity nationally,” said Hamilton. “Because PrEP only protects against HIV, condoms will continue to be an essential tool for preventing other STI and improving public Health and their continued use should be emphasized in any PrEP program.”
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