Project summary


Mathematical modelling of potential risks of any changes to the eligibility criteria for men who have sex with men (MSM) to give blood and plasma is needed, both in the current blood safety context and if alternative risk reduction strategies (e.g. pathogen reduction technologies) are applied in the future. An individual, behavior-based screening approach for all donors (also called a “gender-blind” approach) is advocated by LGBTQ+ groups to permit low-risk MSM to donate blood. Potential approaches to individual risk assessments include deferral based on number of sexual partners or new partners in a certain time period, or an algorithm of sexual risk questions. This mathematical modelling study aims to estimate the risk of an HIV infectious unit of blood being released for transfusion for different possible donor deferral policy options that would permit more MSM to donate blood. The research addresses the questions: What is the estimated residual risk of HIV (i.e. the remaining risk after efforts to identify and control risks have been made) with a 3-month time-based deferral for MSM; What is the residual risk of HIV if selected individual risk assessment eligibility criteria were implemented in Canada? What is the estimated impact on donor deferral vs. donor gains of these changes? 

What was done?

An international team of experts in mathematical modelling refined a model that was previously developed by the same team for time-based MSM deferrals. The model will predict risk and allow comparison of potential policies, using current research data as well as new data arising from the MSM Research Grant Program projects. The model was used to estimate the HIV risk with a 3-month deferral for MSM. The residual risk was modelled for three scenarios 1) most likely – non-compliance-, HIV prevalence- and incidence-rates of MSM are unchanged; 2) optimistic – non-compliance improves by 50 per cent; and 3) pessimistic - non-compliance-, HIV prevalence- and incidence-rates of MSM all double.  

What was found? 

HIV residual risk at baseline was 1 in 36.0 million donations (95 per cent CI 1 in 1,504,907 million, 10.5 million); in the most likely scenario 1 in 34.2 million (1 in 225,534 million, 8.7 million); in the optimistic scenario 1 in 36.0 million (1 in 282,618 million, 9.5 million); in the pessimistic scenario 1 in 16.7 million (1 in 39,469 million, 6.0 million).  All confidence intervals overlapped. With very low modelled risk under a 12-month deferral, the additional risk with a 3-month deferral is very low. This is true even with a pessimistic scenario. 

Opportunities for change

The model has been used to estimate risk for shorter time deferrals and was used to inform Canadian Blood Services’ and Héma-Québec’s application to Health Canada to shorten the deferral period for MSM to 3 months. It can also be used to model risk for changing time deferrals for other infectious risk donor deferrals. Parameters developed for this model were applied in a model to estimate risk associated with removing the MSM time deferral for apheresis source plasma. 

Remaining gaps

A modified approach will be required to estimate risk with plasma donation and a quarantine step, for pathogen reduced products or alternative donor criteria such as individual risk assessment for whole blood donors. The team are also working on a model to estimate risk for plasma donation for fractionated products with pathogen reduction as part of the manufacturing process. 

Research publications and resources 

Davison et al, 2019. Changing the deferral for men who have sex with men – an improved model to estimate HIV risk. Vox Sang 2019, 114:666-674.

O’Brien et al, 2020. HIV residual risk in Canada under a three-month deferral for men who have sex with men. Vox Sang 2020, 115:133-139.

R.E.D. blog post (Dec 2018): Funded research providing evidence needed to evolve eligibility criteria for men who have sex with men

Caffrey N et al. 2022.: HIV incidence and compliance with deferral criteria over three progressively shorter time deferrals for men who have sex with men in Canada. Transfusion 2022; 62(1) 125-34. Article available free online 

Mathematical models of risk - plasma

Dr. Antoine Lewin (Héma-Québec) led a mathematical modelling study to understand the risk associated with source plasma donation by gay, bisexual and other men who have sex with men.

Project completed and published.

Estimating HIV risk

Dr. Trevor Hart (Ryerson University) will estimate the probability of HIV risk with different donor eligibility criteria through biobehavioural and mathematical modelling studies.

Project ongoing.

SexNow surveys

Dr. Nathan Lachowsky (University of Victoria) is gathering data through a large national survey of gay, bisexual and other men who have sex with men to support the development of individual behaviour-based risk assessment and inform alternative eligibility criteria.

Project completed, unpublished.