The model, developed by Valentina Cambiano of University
College London, computes the cost-effectiveness of PrEP for five levels of HIV
risk in HIV-negative gay men, from lowest to highest.
gay man who had had condomless anal sex in the last three months (the risk
criterion for joining PROUD).
gay man who had had condomless sex with at least one short-term or casual
partner in the last three months, rather than any partner.
gay man diagnosed with a bacterial sexually transmitted infection (STI – primarily
gonorrhoea, chlamydia or syphilis) in the previous three months.
gay man who had had condomless sex with at least five short-term partners in
any three-month period during the last year.
In the case of the first group, the model then poses two
1a. HIV testing rates in gay men remain at the current
level, meaning that 94,900 would get tested in the model’s first year (2016).
Furthermore, there is no fall in gay men’s condom use.
1b. Increased awareness of and interest in PrEP leads to a
big upsurge in gay men coming forward for an HIV test, in order to get PrEP,
and 165,800 get tested in 2016. Furthermore, 25% of gay men who were using
condoms start using PrEP instead. This drop in condom use is modelled as a
The model assumes that not everyone offered PrEP and who could
benefit from it will want it; in all scenarios, the rate of acceptance when
PrEP is offered is 50%.
It uses the current UK ‘list prices’ of HIV treatment (Atripla) and PrEP (Truvada) – respectively £6488 and £4331 – and finds that, including
other healthcare costs, the cost of a year’s HIV treatment is about £11,000 and
of PrEP £5000.
In the base-case scenario (1a), the model predicts that out of
all the gay men in England and Wales, 11,800 – only about two per cent – would start
PrEP in 2016.
In scenario 1b, an immediate increase in interest in PrEP would
mean that many more – 81,400 or 14% of the gay men in England and Wales – would
start PrEP. This is partly because the increase in testing that interest in
PrEP prompted would lead to an increase in the number of people who are offered
However even under scenario 1a – no immediate upsurge in HIV
testing – the number of men on PrEP would increase substantially over time. By 2031
under scenario 1a, 46,400 gay men (7%) would be on PrEP. Under scenario 1b it
would be 105,500 (17%).
It is also assumed that, while on PrEP, men continue using it
even if they go through low-risk periods, as long as they continue to have any
condomless sex. PrEP, it is assumed, would be stopped only if they resume 100%
condom use or if their only partner is an HIV-positive primary
partner who is virologically suppressed on antiretroviral therapy.
The model finds that by 2031, the number of men who have sex with men seen for HIV
care would be slowly declining whereas with no PrEP, it would continue to
increase. Stretching out the model to its maximum length – 80 years – the model
finds that over that time, under scenarios 1b, 2, 3 and 4 there would be 84% to
86% fewer HIV infections than there otherwise would have been without PrEP.
Because scenario 1a assumes no annual increase in HIV testing, then the
reduction in HIV infections is somewhat smaller, at 72%. Deaths due to HIV
would decrease by 10% to 13% under all scenarios.
The model finds that even without PrEP, the cost of HIV care
peaks at £800 million by 2036 and thereafter declines to half that amount by about
2070, because of the fact that the great majority of people with HIV are on ART
and virally suppressed.
With widespread PrEP provision, the cost of HIV treatment would
peak at about £600 million in the early 2020s and then dwindle away to £100
million or less by 2070. However, under scenario 1b, unless drug prices fall, the
cost of PrEP would nearly double the peak HIV budget to over £1000 million in
the late 2020s. It would stabilise thereafter at about £700 million. If there
was a 50% reduction in the cost of ARVs this would come down to about £400