Thursday, September 24, 2009

How Well Did The AIDS Vaccine Work?

Lots of people were excited about the hopeful news from Thailand regarding an AIDS vaccine. Medical ethicist Udo Schuklenk, the co-editor of Bioethics, has a sobering reply -- the 31% reduction in rate of infection may just be an fluke result of low sample size. I don't know anywhere near enough about statistics to evaluate this issue myself, but I'll reprint his commentary:
The numbers seems to be speaking for themselves - 31%!!! - but do they? I doubt it. Here's the baseline as reported toward the end of the Los Angeles Times article: 'New infections occurred in 51 of the 8,197 given vaccine and in 74 of the 8,198 who received dummy shots. That worked out to a 31 percent lower risk of infection for the vaccine group.' The 23 additional infections in the placebo arm - out of 16400 overall participants - doesn't seem seem to be a figure that's statistically significant by any stretch of the imagination, no matter how hard the study's spin doctors (it cost 105 mio US$ to conduct the study) try to make it look otherwise. There might be good reason to undertake the same study with a much larger number of participants across the world, but until then, I doubt we have anything to celebrate at all.

For starters the number of people infected in both arms is fairly small (roughly 125 out of >16400, 51 in the active agent arm, 74 in the placebo arm - I doubt that is statistically significant, might be just a fluke).
It'll be a month until the actual study is made public at a conference. Udo criticizes this as a case of "science by press release." His preferred strategy for dealing with AIDS is to put our resources into testing large numbers of people, and treating those who are infected.
Mathematical modelling suggests that the pandemic could be brought to heel within a generation or two by using this strategy. It turns out to be the case that this test-and-treat strategy is also the most efficient means to keep infected people alive and kicking. On my reading of the literature AIDS would turn from a terminal illness into a serious chronic illness that can be efficiently dealt with by means of medical care.
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