Gel offers protection against HIV infection
Chris - Also in the news this week, a vaginal gel which contains the anti-AIDS drug called tenofovir has been found to reduce transmission rates of HIV amongst women by up to 50%. To explain a bit more about the study, which was carried out in South Africa, Salim Abdool Karim is from the University of KwaZulu-Natal is with us now to tell us what he did. Hello, Salim. Thank you for joining us. First of all can you set the scene for us; how big a problem worldwide is HIV? What's the scale of the problem?
Salim - Globally, we have a good idea of what's going on with the HIV epidemic. We know in 2009 that there are 33.4 million people living with HIV and that during 2008, there were 2.7 million new infections, and about 2 million deaths. So globally, the epidemic continues to grow, although it's growing more slowly now than it was some five years ago.
Chris - And just totting those numbers up in my head, that would mean something in the region of 7,000 people a day must be dying of HIV and 7,000 new infections every day. So we need to sort this out. A trial in Thailand suggests that vaccines are only at best 30% effective, so you've been taking a slightly different approach. These gels, how do they work?
Salim - There've been several gels that have been made, and foams and sponges as well, and they've been impregnated with different kinds of chemicals and called microbicides. And the underlying hypothesis is that these chemicals, when put into the genital tract, into the vagina, would prevent HIV from causing infections. Well up to now, in the past 15 years or so, there've been 11 trials of six candidates. None of which has been shown to work.
So, it's been a pretty difficult time in the field to find something that could prevent HIV infections. So we took a different approach. We decided to go with an anti-retroviral drug which is very widely used for treating AIDS and this drug is called tenofovir. It is a standard part of many cocktails of three drugs that are used to treat AIDS. So we put this drug into a gel formulation and we put it into single-use applicators and we did a study of 889 women in South Africa where they were asked to use this gel within 12 hours before sex and within 12 hours after sex. And what we found was that in the half of the women that used the tenofovir gel, there was 38 HIV infections, compared to 60 HIV infections in those women who were using an identical placebo gel. So that translates to a 39% protective effect of this gel.
Chris - And over what period of time were you studying? How long did you look at?
Salim - The first women were enrolled in May of 2007 and we completed the study in December of last year so 2 ½ years in total.
Chris - So if you extrapolated this to making this available to every exposed individual, let's just take Africa as an example, how many cases of HIV do you think you could prevent per year with this strategy?
Salim - We've done some mathematical modelling, creating a hypothetical scenario, as if we were implementing this in South Africa where we have very good data, and we emulated the kind of adherence we got within the study. So within the study, for those women who used the gel most consistently, they had 54% protection and those women who used it least consistently, less than 50% of their sex acts, we saw 28% protection. So what we did is we modelled that. We said, "Okay, what if 40% of the women used it in a consistent way as we observed in our study and 40% used it in an inconsistent way as we observed in our study." And if we did so, then over the next 20 years, we estimate we could prevent 1.3 million new HIV infections and avert just over 800,000 deaths, just in South Africa alone.
Chris - And what cost would that come out at? How much would it cost to implement that?
Salim - Now that's a bit more difficult to calculate. We know the actual cost of the gel is negligible. For the study where we only made a small quantity so we didn't benefit from scale, the actual gel costs about a cent or 2 in US cents. So the cost is not in the gel, but it's in the applicator, the wrapping, and the packaging, and so on, so that for the trial, each application costs us $0.32. If it's produced to scale, we would estimate that it will be substantially less and we worked out that even at the current price of $0.32, it is still cost-effective to implement because the cost of treating somebody who develops HIV infection is so high that even at this cost, to use the gel is more cost-effective than to allow women to get infected.
Chris - Well that brings me on to my last point, which is that the way we treat HIV is with triple therapy. We give people a combination of drugs so that the risk of the virus becoming resistant is reduced. You're using a single agent in this gel. Is there not a risk that we could end up eroding the ability of this agent to prevent HIV because people are being exposed to this as monotherapy?
Salim - Yes. It is a hypothetical concern and certainly, before the results of our study has been looked at in many different ways. These are the first data that have come out now where we can look at whether any of the 38 women who became infected while using tenofovir developed resistance, and the answer was no. We found no evidence of tenofovir resistance.
Chris - Indeed. Salim, thank you very much. That's Salim Abdool Karim who is from the University of KwaZulu-Natal in Durban, South Africa, and he is reporting there the study that he's just published in the journal Science, looking at the use of a vaginal gel which contains the agent tenofovir which seems to be able to reduce by a significant margin the rate of HIV transmission.