The vitiation of consent due to non-disclosure of HIV-positive status has proven particularly intractable for courts, and is in part a measure of the challenge the law faces in keeping up with changes in the science and in treatment. That point could not be clearer that through the proposed evidence in this case, where the very expert whose evidence was relied on by the Supreme Court in R v Mabior, 2012 SCC 47, Dr. Smith, now himself takes a different view of the science.