I doubt anyone is going to use nukes. I think that's just a fantasy. More do since China backs all of these other countries n China isn't about destroying the world when they want money n power. War can start without any nukes. It's already happening and the US have dropped non nuclear bombs in the last few years.Like I said though, any major war would involve nuclear weapons and that would make any disease irrelevant because you can't really classify someone as sick if they're already dead. It would be an extinction-level event for us so I don't think that disease would be something that I'd be worried about at that point. Come to think of it, I don't think that I'll be worrying about anything if I'm killed by radioactive fallout.
I think that I'd be more afraid of Ebola becoming more easily transmitted than COVID becoming deadlier.
Covid was just an example.