HIV transmission and pre-exposure prophylaxis in a high risk MSM population: A simulation study of location-based selection of sexual partners

Epidemic graph diagrams as analytics for epidemic control in the data-rich era

COVID-19 highlighted modeling as a cornerstone of pandemic response. But it also revealed that current models may not fully exploit the high-resolution data on disease progression, epidemic surveillance and host behavior, now available. Take the epidemic threshold, which quantifies the spreading risk throughout epidemic emergence, mitigation, and control. Its use requires oversimplifying either disease or host contact dynamics. We introduce the epidemic graph diagrams to overcome this by computing the epidemic threshold directly from arbitrarily complex data on contacts, disease and interventions. A grammar of diagram operations allows to decompose, compare, simplify models with computational efficiency, extracting theoretical understanding. We use the diagrams to explain the emergence of resistant influenza variants in the 2007-2008 season, and demonstrate that neglecting non-infectious prodromic stages of sexually transmitted infections biases the predicted epidemic risk, compromising control. The diagrams are general, and improve our capacity to respond to present and future public health challenges.

Non-selective distribution of infectious disease prevention may outperform risk-based targeting

Epidemic control often requires optimal distribution of available vaccines and prophylactic tools, to protect from infection those susceptible. Well-established theory recommends prioritizing those at the highest risk of exposure. But the risk is hard to estimate, especially for diseases involving stigma and marginalization. We address this conundrum by proving that one should target those at high risk only if the infection-averting efficacy of prevention is above a critical value, which we derive analytically. We apply this to the distribution of pre-exposure prophylaxis (PrEP) of the Human Immunodeficiency Virus (HIV) among men-having-sex-with-men (MSM), a population particularly vulnerable to HIV. PrEP is effective in averting infections, but its global scale-up has been slow, showing the need to revisit distribution strategies, currently risk-based. Using data from MSM communities in 58 countries, we find that non-selective PrEP distribution often outperforms risk-based, showing that a logistically simpler strategy is also more effective. Our theory may help design more feasible and successful prevention.

Pre-exposure prophylaxis (PrEP) is an effective HIV prevention measure but identifying those most at risk to target for treatment is challenging. Here, the authors demonstrate that non-selective PrEP distribution outperforms targeted strategies when use is not consistent, and/or prevalence of untreated HIV is high.

Preference for daily versus on-demand pre-exposure prophylaxis for HIV and correlates among men who have sex with men: the China Real-world Oral PrEP Demonstration study

INTRODUCTION

This study explores the preference for daily versus on-demand pre-exposure prophylaxis (PrEP) among men who have sex with men (MSM) in developing countries when both regimens are available.

METHODS

From 11 December 2018 to 19 October 2019, we recruited MSM for an open-label real-world PrEP demonstration study in four major cities in China. Subjects selected their preferred PrEP (oral tenofovir/emtricitabine) regimen (daily vs. on-demand) at recruitment and underwent on-site screening before initiation of PrEP. We used logistic regression to assess preference for daily PrEP and correlates.

RESULTS

Of 1933 recruited MSM, the median age was 29 years, 7.6% was currently married to or living with a female; the median number of male sexual partners was four and 6.1% had used post-exposure prophylaxis (PEP) in the previous six months. HIV infection risk was subjectively determined as very high (>75%) in 7.0% of subjects, high (50% to 75%) in 13.3%, moderate (25% to 49%) in 31.5% and low or none (0% to 24%) in 48.1%. On average, participants preferred on-demand PrEP over daily PrEP (1104 (57.1%) versus 829 (42.9%)) at recruitment. In multivariable analysis, currently being married to or living with a female was associated with 14.6 percentage points lower preference for daily PrEP (marginal effect = -0.146 [95% CI: -0.230, -0.062], p = 0.001); whereas the number of male sexual partners (marginal effect = 0.003 [95% CI: 0.000, 0.005], p = 0.034) and a subjective assessment of being very high risk of HIV infection (vs. low and no risk, marginal effect size = 0.105 [95% CI: 0.012, 0.198], p = 0.027) were associated with increased preference for daily versus on-demand PrEP. Among the 1933 potential participants, 721 (37.3%) did not attend the subsequent on-site screening. Lower-income, lower education level, lower subjective expected risk of HIV infection risk and younger age positively correlated with the absence of on-site screening.

CONCLUSIONS

MSM in China prefer both daily and on-demand PrEP when both regimens are provided free. Social structural factors and subjective risk of HIV infection have significant impacts on PrEP preference and use. The upcoming national PrEP guideline should consider incorporating both regimens and the correlates to help implement PrEP in China.