The way to do it, with bacteria anyway, fungus and virus are harder, is to just hoard your DNA points and remain asymptomatic, upgrading things like drug immunity and vectors of infection a lil bit. Then when you've infected every country at least 50%, hit em with all the worst symptoms all at once.

That way, they don't really have any time to fund a cure, and you don't feel powerless once the points dry up in the endgame.