The effect of combination prevention strategies on HIV incidence among gay and bisexual men who have sex with men in the UK: a model-based analysis.

BACKGROUND: In the UK, the number of new HIV diagnoses among gay and bisexual men who have sex with men (GBMSM) has decreased substantially. We aimed to understand the contribution of different interventions in reducing HIV incidence so far; to estimate future HIV incidence with continuation of current policies and with further scaling up of current interventions; and to estimate the maximum additional annual cost that should be spent towards these interventions for them to offer value for money. METHODS: We calibrated a dynamic, individual-based, stochastic simulation model, the HIV Synthesis Model, to multiple sources of data on HIV among GBMSM aged 15 years or older in the UK. Primarily these were routine HIV surveillance data collected by the UK Health Security Agency. We compared HIV incidence in 2022 with the counterfactual incidence: if HIV testing rates stopped increasing in 2012 and the policy of antiretroviral therapy (ART) at diagnosis was not introduced in mid-2015; if pre-exposure prophylaxis (PrEP) was not introduced; if condom use was low from 2012 in all GBMSM, at levels similar to those observed in 1980; and in the first and second scenario combined. We also projected future outcomes under the assumption of continuation of current policies and considering increases in PrEP and HIV testing uptake and a decrease in condomless sex. FINDINGS: Our model estimated a 77% (90% uncertainty interval [UI] 61-88) decline in HIV incidence since around 2014, with an estimated 597 infections ([90% UI 312-956]; 1·1 per 1000 person-years [90% UI 0·6-1·8]) in men aged 15-64 years in 2022. Both PrEP introduction and increased HIV testing with ART initiation at diagnosis each had a substantial effect on HIV incidence. Without PrEP introduction, we estimate there would have been 2·16 times the number of infections that actually occurred (90% UI 1·06-3·75) between 2012 and 2022; without increased HIV testing and ART initiation at diagnosis there would have been 2·18 times the number of infections that actually occurred (1·18-3·60), and if condomless sex was at the levels before the HIV epidemic, there would have been 2·27 times the number of infections that actually occurred (0·9-5·4). If rates of testing, ART use, and PrEP use remain as they are currently, there is a predicted decline in incidence to 388 HIV infections in 2025 (90% UI 226-650) and to 263 (137-433) in 2030. Increases in HIV testing and PrEP use were predicted to accelerate the decline in HIV incidence. Given the quality-adjusted life-year (QALY) benefit and a cost-effectiveness threshold of £30 000 per QALY gained, in order to be cost-effective an additional £1·62 million could be spent per year to increase testing levels by 34% (90% UI 25-46) and PrEP use by 55% (10-107). To achieve that, a 16% reduction in the cost of delivery of testing and PrEP would be required. INTERPRETATION: Combination prevention, including a PrEP strategy, played a major role in the reduction in HIV incidence observed so far in the UK among GBMSM. Continuation of current activities should lead to a continued decline; however, it is unlikely to lead to reaching the target of fewer than 50 HIV infections per year among GBMSM by 2030. It will be important to reduce costs for testing and PrEP for their continued expansion to be cost-effective. FUNDING: National Institute for Health Research under its Programme Grants for Applied Research Programme and Medical Research Council-UK Research and Innovation.