A failure leads to new questions in HIV drug trial

In Africa, a human trial of drug aimed at preventing HIV infection has been halted, because women taking the drug didn't seem to be any more protected against HIV than women taking a placebo. That's happened before with trials of preventative HIV medication. What makes this situation particularly intriguing: These null results seems to be confined to women. When the drug was previously tested in gay and bisexual men, it reduced their chances of being infected with HIV by between 44% and 73%, depending on how faithfully the men stuck to the drug regimen.

Maggie Koerth-Baker is the science editor at BoingBoing.net. She writes a monthly column for The New York Times Magazine and is the author of Before the Lights Go Out, a book about electricity, infrastructure, and the future of energy. You can find Maggie on Twitter and Facebook.

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lmnop

Different strains prevail in the US and Africa. Type B is dominant in the new world and Europe, and my understanding is that this strain is most easily transmitted through the blood, making anal sex riskier. African varieties tend to be easily spread through mucosa, implicating vaginal sex. If the heterosexual testing was done in Africa (which is stated in the article), but homosexual and bisexual testing was done in the US/Europe (I assume that such testing would be more difficult to do in Africa because of reluctance to identify as homosexual or bisexual), the results could be explained.
Anonymous

So it perhaps works by thickening the mucosal walls in the glans/penis (the same mechanism which makes circumcision “effective”, building up a callous on what is normally very thin and permeable tissue, in addition to outright eliminating some of it), or some other physical mechanism that is gender limited?
bigomega73

I haven’t read the full study on gay/bisexual men, but I wonder if it took into account what sexual role they were performing during anal sex. Since not all gay/bisexual men are the receptive partner during sex, their risk would be much less than those that are the receptive partner. And I would assume the risk would be about the same for receptive partners as it would be for women, since both are receiving bodily fluids directly into their bodies. I think in order to have an adequate comparison, they would need to only study gay/bisexual men who only performed as the receptive partner.
Lobster

I’m assuming it also protects heterosexual men, right?
- Antinous / Moderator
  
  I’m assuming it also protects heterosexual men, right?
  
  The funny thing about science is that it doesn’t always return the same conclusions as assumption. So, no.
- JM
  
  Duh, heterosexual men can’t get infected. This disease only affects gay & bisexual men, women and other creatures unworthy of God’s eternal love.
  
  [/sarcasm]
- Maggie Koerth-Baker
  
  Well, that’s not a given, since what we’re really likely talking about here is vaginal sex vs. various sorts of non-vaginal sex. The earlier study was specifically done with men who self-identified as gay or bisexual. It’s possible the drug would be as effective in straight men (if the effectiveness factor comes down to having a penis), but it’s also possible that the drug wouldn’t protect straight men (if the effectiveness factor comes down to what you’re doing with your penis). Could go either way. Which is part of what makes this interesting.
Anonymous

Once again, they don’t acknowledge a negative result. The gay men were given condoms and public health tips. The women were given oral contraceptives and drugged lube. Quite a few became pregnant, so obviously compliance was not great for the contraception.

If the reduction in male infection is statistically significant, it is primarily because of condom use. Men have less need to avoid condom use, as ‘slightly increased sensation’ is less of an incentive than pregnancy.
Mister44

How much would it suck to be in an Anti-HIV drug study and given the placebo?
Anonymous

You could assume it would also protect heterosexual men, but they probably did not study it in that group of people. Without a study, they cannot make the claim.
Anonymous

The result could also be the product of different rates of infection in the different populations. If men who have sex with men are at a high risk of infection, a small protective effect from treatment might yield a significant result.

If women are at lower risk, the same small protective effect might not make much of a difference.

Pulling numbers out of the air, reducing a 50 in 100 risk by 50 percent gives you a 25 percentage point drop in absolute risk. Reducing a 2 in 100 risk by 50 percent is a 1 percentage point drop in absolute risk. This smaller drop in absolute risk might be harder to pick up in a study.

I have no knowledge of infection rates in the populations studied, but as a general point the benefit you get from a preventative treatment will depend on your baseline risk.
redstarr

I wonder if part of it might be due to compliance issues. In a lot of the world, women are more powerless and might have not used the medicine as often as they should have or as often as they reported. I could see women having less control over their sexual partners than straight or gay men and feeling more pressure to not take or be seen taking the medication. If you’re a girl in a lot of places, using an anti- HIV drug could make your husband really angry or suspicious and that’s a risk you might be afraid to take. I’ve heard that promoting condom use in a lot of places runs into those types of social issues and it might make sense for these drugs to be running into that,too.
Shift

This is why I love BB. Fascinating. Thanks for sharing.
redstarr

Also, might have been interesting to see the results for homosexual women. That might help clarify if it’s the female anatomy itself that’s the variable or partly the sexual acts that involve a penis that are the variable.