Population-level effectiveness of pre-exposure prophylaxis for HIV prevention among men who have sex with men in Montreal: a modelling study of surveillance and survey data

BackgroundHIV pre-exposure prophylaxis (PrEP) has been recommended and partly subsidized in Quebec since 2013. We aimed to evaluate the population-level impact of PrEP on HIV transmission among men who have sex with men (MSM) in Montreal over 2013-2021. MethodsWe used an agent-based mathematical model of sexual HIV transmission to estimate the fraction of HIV acquisitions averted by PrEP compared to a counterfactual scenario without PrEP. The model was calibrated to local MSM survey and cohort data and accounted for COVID-19 pandemic impacts on sexual activity, prevention, and care. To assess potential optimization strategies, we modelled hypothetical scenarios prioritizing PrEP to MSM with high sexual activity or aged [&le;]45 years, increasing coverage to levels achieved in Vancouver (where PrEP is free-of-charge), and improving retention. ResultsOver 2013-2021, the estimated annual HIV incidence decreased from 0.4 (90% credible interval [CrI]: 0.3-0.6) to 0.2 (90%CrI: 0.1-0.2) per 100 person-years. PrEP coverage in HIV-negative MSM remained low until 2015 (<1%). Afterward, coverage increased to a maximum of 10% (15% of those eligible for PrEP) and the cumulative fraction of HIV acquisitions averted over 2015-2021 was 20% (90%CrI: 11%-30%). The hypothetical scenarios modelled showed that PrEP could have averted up to 63% (90%CrI: 54%-70%) of acquisitions if coverage reached 10% in 2015 and 30% in 2019, like in Vancouver. InterpretationPrEP reduced population-level HIV transmission among Montreal MSM. However, our study suggests missed prevention opportunities and provides support for public policies that provide PrEP free-of-cost to MSM at high risk of HIV acquisition.