The recent Lancet reports paint a complicated picture: if I read them correctly, the inference that vector might enhance sero-conversion is muddied by the finding that circumcision status might also have played a role in sero-conversion (men with higher rates of adenoviral immunity were also, coincidentally, less likely to be circumcised).
What is clear, from what I gather, is that this is a good example where rigorous preclinical testing, coupled with rigorous trial design, permits meaningful interpretation of (unfortunately) negative human trial results. As Merlin Robb notes in a commentary accompanying the Lancet reports "the predictive value of the non-human SHIV-challenge model is not supported by this experience. The benchmarks for advancing candidate vaccines to efficacy testing and the priorities for vaccine research have been re-examined."
Well-designed studies, supported by rigorous preclinical testing, should always produce valuable, findings– like the unexpected "found figures" in the bark of a tree (photo credit: Readwalker, Found figures, 2006)