The prophylactics should not affect clinical trials a lot. Obviously the organizers need to track who also takes prophylactics. It would be unethical to only enroll participants (especially those at higher risk) who don't take prophylactics because they could get the placebo and then they have zero protection.
Everything else is just a question of the statistical signal detection. Those Studies are planned and designed to provide such a signal, with all we know about HIV prevalence (which is already quite low, in most industrial countries, speaking statistically and for the overall population) and the effectiveness of prophylactic treatment.
Also what I'm hearing the prophylactic treatment is not much fun either... I rather see the danger of participants getting the placebo, drop the prophylactics and think they are protected...
Everything else is just a question of the statistical signal detection. Those Studies are planned and designed to provide such a signal, with all we know about HIV prevalence (which is already quite low, in most industrial countries, speaking statistically and for the overall population) and the effectiveness of prophylactic treatment.
Also what I'm hearing the prophylactic treatment is not much fun either... I rather see the danger of participants getting the placebo, drop the prophylactics and think they are protected...