In August 2011 because of new data from other clinical trials, NIAID shifted the focus of the study to determine whether vaccination was also able to prevent HIV infection.
As a result of this change to the research questions, NIAID also announced an expansion in the desired enrollment to a total of 2200 participants.
[citation needed] HVTN 505 is a phase IIB, randomized, placebo-controlled, double-blind clinical trial.
[5] The study's enrollment target was expanded to 2,200 in 2011 to gather additional data which would allow researchers to determine the extent to which the vaccine regimen also protected against infection.
[6] When the vaccinations were stopped on April 23, 2013, the study had enrolled 2,504 volunteers at 21 sites in 19 cities in the United States.
[7][8] The criteria about circumcision and adenovirus antibodies were added as a precaution in light of the results of the prior STEP study.
[12] These differences are not statistically significant, but all participants were asked to remain in the study for the full-time planned so that researchers can monitor their safety and continue to learn as much as possible.
[16] In the STEP study, participants who received the vaccine contracted HIV at a rate that was significantly higher than placebo recipients.
These include data used in the original efficacy analysis,[20] as well as recent studies describing the effects of the vaccines used on the immune responses of participants.