Assume that the future can change based on your actions, so any historical information that you bring along with you from the intervening 25 years may quickly drift out of the new realities history.
Edit: also assume that you can be given a healthy 21-year-old body if you want or take your previous self’s place.
Further, identification will be provided for you if you were not born at that time.
Given that the AIDS epidemic was still in full swing at the time, just being able to teach medicine makers how to make pRep would make you a billionaire just from the licensing fees.
What’s that? Profilactic?
You can just take back the experimental vaccine and save some people.
Prep is an anti-hiv pill.
If you engage in practices likely to expose you to HIV you should use prep.
If you have pRep in your system and you are exposed to HIV there is a high likelihood that the pRep will destroy the HIV and prevent the infection from ever taking hold.
Of course, it won’t do anything to protect you from the other potential negative consequences of risky behaviors that would expose you to HIV, but considering that it helps protect you from one of the worst potential outcomes it’s essentially a godsend.