And that's one of the focal points of why I thing this episode is so poor and endemic of the problems Trek starting having, particularly when it comes to Braga's writing. He doesn't seem to consider anything beyond an episodic nature or what he's writing SAYS things and has CONSEQUENCES.
This episode shows that if someone is suffering from simple illness all it takes is an absent-minded shot of a hypospray to cause a virus that can "de-evolve" anyone and everyone. It created an AIRBORNE pathogen! All from ONE. Single. Hypospray shot. The episode would still have mountains of problems if what kicked this off was something vastly more complex but at least it wouldn't seem like this happening wasn't "so easy."
Fine, I'll accept that this "could happen" that there's some aspect to genetics, DNA, RNA or whatever at some complex level beyond our current understanding that'd allow for this. Fine. That's Star Trek science by and large.
But it's utterly stupid that it could happen so easily.