PrEP and TasP modelling shows need for optimization

posted on April 30, 2021

Gay, bisexual and other men who have sex with men (MSM) have been disproportionally affected by the HIV epidemic in British Columbia (BC). Since 2010, Treatment as Prevention (TasP) has been adopted as a public health policy in BC to maximize health care engagement of people living with HIV and improve virologic suppression, and as a result, to reduce secondary new infections. However, TasP has been relatively less responsive in reducing HIV transmission among MSM than in other populations in BC, which calls for further optimization and combination with other preventive strategies.

Pre-exposure prophylaxis (PrEP), in the form of daily oral combination of tenofovir and emtricitabine, has been shown to be protective against HIV infection among MSM, with an efficacy ranging from 44% to 97% from clinical trials. In Canada, BC was the first province to providing fully-subsidized PrEP for eligible individuals in 2018. By the end of 2019, more than 5500 MSM has had been enrolled in BC’s PrEP program, and more than 3300 MSM were dispensed PrEP in the fourth quarter of 2019.

We built a mathematical model to simulate the HIV epidemic, considering different age (<30 versus ≥30 years old) and risk-taking behaviour (had ≤10 versus >10 partners and condomless anal intercourse acts in the last 6 months) among MSM in BC. The model projections were used to evaluate the long-term impact of the current TasP and PrEP programs, and the impact of possible optimization of different TasP and PrEP components. We aimed to reduce the HIV incidence rate below the World Health Organization (WHO) incidence threshold (one new HIV case per 1000 susceptible MSM), which is known as the goal to eliminate HIV as a public health concern. We also aimed to reduce the effective reproduction number Re, which is a number that reflects the average number of new infections an individual can generate. If this number Re is below one, disease elimination can be achieved in the foreseeing foreseeable future.

The model was calibrated to fit the HIV prevalence, new HIV infections, HIV continuum of care and PrEP program among MSM in BC up until 2019, and simulations were projected for 2020-2029. By the end of 2029 under the current TasP and PrEP programs, the model predicted the HIV incidence rate to be 1.2 (2.5th-97.5th percentile 0.9-1.9) per 1000 susceptible MSM and Re to be 1.3 (1.0-1.9). Only by optimizing all aspects of TasP and simultaneously providing PrEP to MSM at a higher risk of HIV acquisition, the HIV incidence rate can drop below the WHO threshold (as low as 0.4 (0.3-0.6) per 1000 susceptible MSM) and Re as well (as low as 0.7 (0.6-0.9)). Further improving TasP and focusing on providing PrEP to those <30 years old could achieve comparable results. Our model provides important results to inform the development of public health policies to address the HIV epidemic among MSM in BC and in other similar settings.

BC Centre for Excellence in HIV/AIDS

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PrEP and TasP modelling shows need for optimization

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