Just like 1974 said this is far from legitimate. Just because something is possible it does not mean its legitimate.
I doubt we will see biological warfare or widespread chemical warfare anytime soon. The global repercussions for any country that would do this would be extreme. This is in line with dropping nuclear bombs (in some respects worse) and way too hard to contain or target a certain group of people with when we talk about biological warfare.
I also doubt anyone wants to top maniacs like Hitler as the evil villain in history books. Who would support a government who would take these kind of steps to further their own agenda? Only people with a complete lack of ethics and long term thinking and this very small and obviously rather “simple minded” crowd would also get exploited and discarded whenever necessary by such a government.
Could this happen in an undercover operation? Yes, of course. But countries like the US are too dependent on China for this, Russia does not have the resources to occupy much more than a few smaller countries next to them and China does not need to do this because the old west falls anyway in the coming years and are already dependent on China.
Its not impossible but a scenario I do not really prepare for. I wont be in any urban center that would be targeted and once reports for whatever disease spread I go on lockdown at my homestead anyway.
Alea iacta est ("The die has been cast")