Mathematical modelling of the influence of serosorting on the population-level HIV transmission impact of pre-exposure prophylaxis
Date
2021
Authors
Wang, Linwei
Moqueet, Nasheed
Simkin, Anna
Knight, Jesse
Ma, Huiting
Lachowsky, Nathan J.
Armstrong, Heather L.
Tan, Darrell H.S.
Burchell, Ann N.
Hart, Trevor A.
Journal Title
Journal ISSN
Volume Title
Publisher
AIDS
Abstract
Objectives: HIV pre-exposure prophylaxis (PrEP) may change serosorting patterns. We
examined the influence of serosorting on the population-level HIV transmission impact
of PrEP, and how impact could change if PrEP users stopped serosorting.
Design: We developed a compartmental HIV transmission model parameterized with
bio-behavioural and HIV surveillance data among MSM in Canada.
Methods: We separately fit the model with serosorting and without serosorting [counterfactual;
sero-proportionate mixing (random partner-selection proportional to availability
by HIV status)], and reproduced stable HIV epidemics with HIV-prevalence
10.3–24.8%, undiagnosed fraction 4.9–15.8% and treatment coverage 82.5–88.4%.
We simulated PrEP-intervention reaching stable pre-specified coverage by year-one and
compared absolute difference in relative HIV-incidence reduction 10 years postintervention
(PrEP-impact) between models with serosorting vs. sero-proportionate
mixing; and counterfactual scenarios when PrEP users immediately stopped vs. continued
serosorting. We examined sensitivity of results to PrEP-effectiveness (44–99%;
reflecting varying dosing or adherence levels) and coverage (10–50%).
Results: Models with serosorting predicted a larger PrEP-impact than models with sero-proportionate
mixing under all PrEP-effectiveness and coverage assumptions [median
(interquartile range): 8.1% (5.5–11.6%)]. PrEP users’ stopping serosorting reduced
PrEP-impact compared with when PrEP users continued serosorting: reductions in
PrEP-impact were minimal [2.1% (1.4–3.4%)] under high PrEP-effectiveness (86–
99%); however, could be considerable [10.9% (8.2–14.1%)] under low PrEP effectiveness
(44%) and high coverage (30–50%).
Conclusion: Models assuming sero-proportionate mixing may underestimate population-
level HIV-incidence reductions due to PrEP. PrEP-mediated changes in serosorting could lead to programmatically important reductions in PrEP-impact under low PrEP effectiveness.
Our findings suggest the need to monitor sexual mixing patterns to inform
PrEP implementation and evaluation.
Description
Some of the model parameters in the current modelling
article drew on estimates published in Wang et al. 2019
(https://doi.org/10.1093/aje/kwz231). We acknowledge
the Engage study and its funders (Canadian Institutes of
Health Research (CIHR) Team Grant [TE2-138299];
CIHR Canadian HIV Trials Network [CTN 300];
Canadian Foundation for AIDS Research [Engage];
Canadian Blood Services [MSM2017LP-OD]; Ontario
HIV Treatment Network (OHTN) [1051]; Ryerson
University [no related grant number]; and Public Health
Agency of Canada [4500370314]), which supported the
independently published results in Wang et al. 2019
(https://doi.org/10.1093/aje/kwz231).
We would like
to thank Kristy Yiu for supporting submission and project
coordination, and Steven Tingley for helpful discussions
surrounding model structure.
Keywords
HIV, MSM, pre-exposure prophylaxis, serosorting, sexual mixing patterns
Citation
Wang, L., Moqueet, N., Simkin, A., Knight, J., Ma, H., Lachowsky, N. J., Armstrong, H. L., Tan, D. H. S., Burchell, A. N., Hart, T. A., Moore, D. M., Adam. B. D., Macfadden, D. R., Baral, S., & Mishra, S. (2021). “Mathematical modelling of the influence of serosorting on the population-level HIV transmission impact of pre-exposure prophylaxis.” AIDS, 35(7), 1113-1125. DOI: https://doi.org/10.1097/QAD.0000000000002826