Maybe I'm reflexively anti-conspiracy-theory, but among all the methods to assassinate someone, I don't see infecting them with influenza B and MSRA as a feasible one. How exactly do you infect someone with influenza B, and how do you know they'll die. Most people don't die from the flu. Heck, a lot of people take the annual vaccine (I do). Why would you choose the flu as a weapon?
I don't think so. A few years ago I had some severe allergic reaction to some food stuff and I was on prednisone for half a year. The initial daily doses were huge (about 100 mg). I don't remember I had any severe colds, or any colds at all. I'm not 100% sure, but at least if I had any cold, it was not bad enough to stay in my memory. Certainly not to send me to the hospital.
The funny thing about colds is that you don't die from them, you die from the immune response. That's why the first effective countermeasure to Covid-19 was dexomethasone, an immunosuppressant. Even before Covid-19 became a pandemic, and it was just a thing in Italy, I read about some asthma inhaler as being helpful, and asthma inhalers are just immunosuppressants.
In principle if you give someone absolutely massive doses, then maybe a cold just kills them. But, based on my sample of 1, you would need lots of pills to do that. The highest prednisone dose is 20 mg. Five pills will not make you more vulnerable to a cold. How do you make someone take ten pills without them knowing? And do that for a few days in a row? And there's no guarantee that 10 pills daily will do the job.
not that i believe.. but if we are entertaining the idea assuming they did it..
i would bet they are are not using prescription drugs, they would likely get the stuff pure and use that instead.. so you could deliver a much bigger dosage of the drug more easily, but i guess that likely side effects would kick in.. there may be a limit on how big the dosage can be and they need to watch out, some people are more sensitive then other..
also they would need to keep then on the drugs for several days up to weeks.. that would need massive access to the person being targeted..
now, if you have the level of access to pull this off then there are much easier ways to do it..
But if you put your conspiracy glasses on, you'll immediately see the plausible deniability benefits of the method (also, it's not like you've only got one shot at this...)
[0]: https://news.ycombinator.com/item?id=40230790