Three trials were stopped in 2007. The STEP trial showed that those with pre existing exposure to adenovirus ad5 had a higher infection rates on the vaccine versus placebo. Those infected were also mostly uncircumcised. Those who were not exposed to ad5 prior to the study and who were uncircumcized actually showed lower infection rates.
Extra ad5 in those ad5 positive at baseline may have increased cd4 activation that made those people were prone to hiv infection.
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