Merck plans to tell thousands of people who volunteered to test an experimental AIDS vaccine whether they received the actual shot or a placebo. The vaccine may have actually raised the risk of HIV infection.
Two international trials of the vaccine were halted in September after it became clear that the vaccine did not prevent infection. In early November, researchers saw worrying indications that the vaccine could raised the risk of HIV infection, although they have asserted that the vaccine itself could not cause an infection.
In many tests of new drugs, neither the researchers nor the volunteers know who gets the actual drug and who gets a placebo, in order to avoid any bias in determining how well the treatment works.
* Reuters November 13, 2007