Vaccines are supposed to stop you getting sick. But in one of the biggest HIV vaccine trials yet, not only did the vaccine not work, it may have made people more susceptible to infection. It may not even be the only HIV vaccine to backfire in this way.
The STEP trial was one of only two so far aimed at preventing HIV infection. Since 2004, 2675 people at high risk of contracting HIV have received either a vaccine made by US drugs giant Merck, or a placebo, at 19 sites in North and South America and Australia. They also got…
