Like you said, the big governments would not even need to go that far if they wanted to do us actual physical harm. Most of them can just press a button to erase most countries from the surface of the planet. If we want deadly viruses, bacteria or toxins, we have plenty of them available from just natural evolution, that have decimated sizeable numbers of people in the past, and that we've been studying and archiving for decades in labs to understand them and recognise them faster if they reappear. They just need to release a sizeable sample of those if they want to eradicate a few cities, as well (black pest, anyone?)Sadly i do believe that a more dominant mutation will come out in the upcoming months due to the selfish people who are putting others at risk because they refuse to take the vaccine causing the virus to go into a harder mutation.
If we all just cooperated from the beginning and not listening to all the conspiracies things that come forth from every disaster events, we might be in a very different position than we are now. People are just too selfish and think that the "Goverment" wants to murder them all. If the Goverment trully wanted to eradicate as many humans as possible, believe me we wouldn't all be here, they could just release a manufactered deadly virus into the air untreceable and we all would fall like domino stones. There are many ways that could take many people out if they wanted. Like others have said, its selfish not to take the vaccine, as it meant to stop the virus but instead it will mutate by all the naysayers that in the end will bring only more hurt than good.
Why go the expensive way of engineering something when nature has already done it for you, basically for free? (well technically not free, the price was the lives those things already took during their own outbreaks, but you know what I mean, it's not a direct cost for us anymore)
At any rate, believing they actually want to do anything remotely close to that kind of bad to us is delirious at best. They are far too much in need of us to produce their wealth to take any risk like that (especially because it would affect them, too), and money is a far better way to control people when you have a good control over it like they do. They very much know that, they're not stupid.