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PrEP will need high adherence, high effectiveness and high coverage in specific populations to be affordable in the US, New York study finds
Gus Cairns, 2014-10-01 10:10:00

A study based on New York City that modelled pre-exposure prophylaxis (PrEP) uptake there has found that in order to be affordable, PrEP would need to be tightly targeted at gay men at higher risk of HIV infection. Within this target population, it would need high levels of usage.

A reduction in the price of Truvada – the tenofovir/emtricitabine combination pill which is currently the only one used for PrEP – would also help. The model ran through a number of scenarios and found that while PrEP could be potentially cost-effective at Truvada’s present price, it would only become cost-saving if its current US price was halved. Even then, it would require near-universal uptake in higher-risk gay men.

Like all mathematical models, this one has to start with assumptions about PrEP’s likely uptake and effectiveness. Drug-level monitoring studies show that PrEP is highly effective (over 96%) in people who are even moderately adherent. This model uses a base-case scenario of PrEP having 44% effectiveness, which was what was seen in the original iPrEx study in gay men (effectiveness was 50% in the open-label extension of this study).

An updated analysis of adherence by site, however, presented at the recent third IAPAC summit on treatment as prevention, shows that trial participants in the US sites managed adherence of approximately 80% at any one time or 67% over time, suggesting that effectiveness rates in US populations could be more like the 75-80% seen in the Partners PrEP study in heterosexual couples. If effectiveness was 75%, then PrEP would become cost-saving with somewhat lower coverage and would be potentially cost-effective, even at Truvada’s current price, in all gay men.

There is no scenario in which PrEP was cost-effective if offered to high-risk heterosexuals, and almost none if it were offered to people who inject drugs. In the former case, this is because HIV incidence in the US is not sufficient even among high-risk heterosexuals to justify the cost of PrEP – you would need to give a lot of people PrEP to avert one infection – and in the case of people who inject drugs, while they are at very high risk of HIV, there are not enough of them in New York City to make a PrEP programme cost-effective in terms of the number of infections it would prevent.

As the researchers say, this does not preclude offering PrEP to members of these groups who are at exceptionally high risk of acquiring HIV, for instance heterosexuals in a sero-different relationship with a partner who is off treatment or has adherence difficulties, or people who inject drugs who also have sex with men.