In the latest setback in the search for an HIV vaccine, a major trial has closed down after the experimental vaccine failed both to prevent HIV transmission and to reduce viral load in those who contracted the virus. An independent review board found that more people receiving the vaccine became infected with the virus than those receiving the placebo—although this difference was not statistically significant and may have been the result of chance. Called HVTN 505, the Phase IIb study was conducted by the HIV Vaccine Trials Network, which is sponsored by the National Institute of Allergy and Infectious Diseases. Beginning in 2009, it enrolled 2,504 men who have sex with men and transgendered people from across the United States. The trial follows on the heels of the RV 144 vaccine trial, which reduced infection rates among heterosexuals in Thailand by 30 percent, but which was itself brought to a close in 2009 because its protection rate was still not high enough.