NYT AIDS story

I think the New York Times is a pretty good newspaper in general but this story on an AIDS prevention gel for women is just dreadful. It starts:

The best AIDS-prevention news in years was released here last week at a world conference on the disease: a vaginal gel, called a microbicide, that can be used without a man knowing it, gave women a 39 percent chance of avoiding infection with the deadly virus.

Thirty-nine percent is, obviously, not perfect, though the women in the South African trial who used the gel most faithfully did better, achieving 54 percent protection.

It is completely unclear what the 39% and 54% are referring to and this is not explained in the remainder of the story. I suspect this is because the reporter had no clue. But if he can't explain what these numbers mean they shouldn't be in the story.