Yes I knew. I was paid $50 or $100 per visit I believe (this was 15 years ago). Iirc I received a basic check up first and then over time 2 or 3 doses of vaccine. most visits were a quick blood draw. The study lasted over a year and I think I probably went in about 1-2x/per month.

They did explain the risks. That is a normal part of the consent process for any human subject participating in a study.

To be clear, there was NO RISK of being exposed to HIV, if that is your concern. The vaccine didn’t contain any HIV.