Ah, that’s what I thought but I just wasn’t sure. Okay, the gender isn’t really important to the story. My original intent was to make him an African American man, which in fantasy/sci-fi are usually in non-important roles, or stereotypes. Or quite often stereotypical minor roles.
One last comment, I always like a good standalone story, everything is turning into franchises now, rather than giving new(and more diverse) characters their chance to have their story told. Anyway, it is a world filled with superheroes and powered people, that does suggest it could easily be a franchise.
Anyway, onto the story. While the points you bring up are things should definitely be answered, most of them probably shouldn’t be included in the logline, but if you’re curious I’ll explain a little. The superhero does have superpowers, but she isn’t immune to diseases. And there are more superheroes than her, which is why in my first version I referred to her as the “world’s greatest superhero”, so not everyone else is normal. As for how she gets infected in the first place, I will say that a villain got a hold of the plague and modified it to rid him/herself of this hero, but the MC still is guilty because he created such a deadly plague in the first place.
And the last thing, he does commit a terrorist attack by releasing the plague, and he goes to prison for that reason, but again I think saying that he breaks out of prison is enough for the logline. As for why he engineered the plague, I haven’t the foggiest clue yet.
I do agree, that the story that is presented as her backstory in this logline is a story in itself.

Revision: When a bio-terrorist’s engineered plague is modified to infect a superhero, the convict breaks out of prison to create a cure for the hero?she loves.