The article is interesting in terms of the fairly clever science but doesn't point out the really amazing success of the PrEP trials. A variety of PrEP trials have been taking place including the use of oral emtricitabine/tenofovir (Truvada) tablets in a Western context (the PROUD and iPrEx trials) and the CAPRISA 004 pericotal tenofovir gel trial in South Africa.

The basic idea is this: using antiretrovirals as a preventative strategy. Take one of the current combination HIV antiretrovirals (emtricitabine/tenofovir, for instance) and administer it to patients who are at risk of getting HIV (drug users, men who frequently have sex with men without condoms, people with HIV positive partners).

The trials have been really successful. Adherence has been high. Side effects have been low and controllable. Those on PrEP combined with a frequent testing regime don't show signs of increased risk behaviour.

Because of the success of the trials, the WHO and the CDC are now recommending that people in high-risk groups start taking a daily PrEP - and in the US, plenty of doctors are now prescribing it for some of their high-risk patients.

Here's where it gets more interesting: the patents on Truvada, the emtricitabine/tenofovir combo tablet, expire in 2016. Currently Truvada as PrEP is an expensive proposition: in the US costing between $8,000 and $14,000 according to government figures. Low-income users of PrEP can get financial subsidy from Gilead Sciences, the manufacturer of Truvada—Gilead don't consider Truvada as PrEP to be a major financial gain for them so they are providing subsidies in the US for PR reasons.

Countries with national healthcare systems are probably going to try and hold off for long enough for Truvada as PrEP to go out of patent and then wait for generics to come on the market.

That's when things get interesting. Currently, $8-$14k for a preventative is too much even for rich countries to consider. It wouldn't pass the United Kingdom's NICE process on cost-benefit grounds. But imagine if it cost a few hundred dollars a year rather than a few thousand. Then the cost-benefit analysis becomes a lot easier. In the UK, we currently pay around £300,000 to treat an HIV positive patient over the course of their lifetime. A few hundred dollars a year for those most at risk as a preventative cuts a lot of healthcare costs.

Imagine the scenario: in the West, anyone who wants to get on PrEP would be able to do so with minimal fuss—it'd be cheap enough that reasonably well-off people could pay out of pocket, and it'd be covered by insurance and national health coverage. It becomes as routine for the younger gay male population as the contraceptive pill became with women. This provides the sexually responsible a second line of defence, and the less sexually responsible a pretty effective (90%+, if the iPrEx study is to be believed) first line of defence. It's backed up by a routine testing and education regimen that catches infections early to prevent spread. The challenge is how to roll it out cheaply in Africa: finding a way to do bulk production of the drugs and ensure they are being taken responsibly. The hard bit there isn't making the pills but building the public health infrastructure. Still cheaper than the economic costs of mass HIV infection though.

PrEP isn't a vaccine but it might end up functioning like one: reducing the transmission rate in affected communities over the long run means less people needing treatment and decreasing the overall risk of infection. And come 2016, once the patents are gone, it'll be cheap. There's lots of people wringing their hands about PrEP mostly for dumb moralistic reasons but it looks like the first major innovation in HIV that might actually have a shot at working.