A preventative HIV medication may help protect those who take it against contracting the herpes virus as well. This extra protection was discovered during a randomized trial in which participants took drugs to prevent HIV infection as the central focus for the trial.
Participants in the trial took daily doses of medication that included tenofovir, which has been shown to lower the risk of HIV contraction by 75 percent. Further analysis revealed the reduced risk of herpes contraction.
This extra protection is thought to be especially beneficial for couples where one of the partners has HIV and the other does not. The presence of herpes is known to increase the risk of HIV contraction. According to research, this increase can be anywhere from three to six-fold.
"Antibodies are a way for your body to highlight what doesn’t belong. When one antibody reacts with two different antigens, this is called cross-reactivity; this is what happens with HSV-1 and HSV-2. Think of antibodies as highlighting and creating handles for T-cells to gobble up. T-cells are what eat what doesn’t belong. B-cells and plasma cells are what produce antibodies.
Viruses are coated in proteins, same as an egg is surrounded by an eggshell. So when you get a vaccine, imagine it like it’s giving you pieces of the eggshell so that your body recognizes these pieces by creating antibodies. If it is exposed to it again, it’ll be able to recognize the eggshell and fight it off.”
Note: this is a very simplified explanation because it doesn’t cover the innate responses, how antibodies are made, etc.