Sci-fi protagonist uses a virus to alter their genetics for better vision. <2006. Mystery. YA?

[David]

I can’t remember much about the plot other than I think it was a mystery book. It was probably YA.

I remember the protagonist intentionally infected themselves with a virus that altered various parts of their biology by messing with their genes. They got sick for a while and emerged on the other side with better eyesight and some other features. I think the protagonist was being followed or hunted?

I would have read the book in the early 2000’s so it can’t be any newer than 2006 or so.