How efficacious does a microbicide need to be?

In the context of planning clinical trials for anti-HIV vaginal microbicides, some authors use mathematical modeling to demonstrate efficacy, with changing numbers based on differing assumptions. Using these simulations, researchers can demonstrate that even moderately effective microbicides can have a major impact on HIV transmission: “a 60% efficacious product, available to 20% of women and used in 50% of sex acts when a condom is not used could prevent 2.5 million new HIV infection over 3 years in high incidence countries.”[1]

The use of a microbicide is demonstrably a great benefit to the hypothetical population mentioned above. For the many, it clearly saves lives and provides protection to a part of the population that previously had few options. However, what if you were one of the women who used the product correctly and diligently whenever you were supposed to, but you were part of the other 40%, the 40 out of every 100 women for whom the microbicide failed to protect against HIV? You might feel cheated or lied to, that this product was supposed to protect against HIV and it didn’t for you. The accompanying literature explains that the product is not 100% effective, but the product is also put out in the population, because it does save lives. Just not yours.

Every product has this issue; none are 100% effective. So 1 out of every 10 or 100 or 1000 or more becomes infected or isn’t protected. But is 60% efficacy sufficient to justify a trial? Would you use it and depend on it? And if you wouldn’t, should others?

---

[1] Watts C, Kumuranayake L, Vickerman P, Terris-Presholt F. 12 – 15 May 2002. Microbicides 2002, Antwerpen, Belgium [Abstract] C319, 68.3