Which science are you talking about. The “science” that claims that human caused global warming is a done deal or the science that asks questions and strives for the truth.
Conservative science, which is a procedure for discovering accurate facts about reality.
How many out of 650 or so were exposed to HIV during the study period? If it’s 600, and none of them has contracted the virus (after a suitable waiting period), then it seems this is a very successful prevention regimen.
If only 40 were exposed, it was still a successful prevention for them. However, there could be other factors ... Maybe they were in excellent health to start with. Maybe their choice of sexual activity is less likely to transmit HIV. Etc.
Ask a question. Hypothesize an answer. Design and conduct an experiment. Evaluate the results. Repeat. SCIENCE.