I watched two more vanden bossche vids, and he's posted a synposis of his concerns, there is something I just don't get in his argument, as if a piece of the explanation is missing.
I generally thought viruses weaken when they mutate, as that improves the chance of propagating themselves, bit like the common cold, you tend to carry on your daily activites rather than be bed-bound. His theory seems to be the virus could become worse as then people will shed it more, I don't think he has explained the science in a way people can fully understand it, certainly I can't despite trying a fair bit!
I did think if the vaccines are focused on 1 part of the spike protein, compared to natural immunity which would be broader and target more parts, then that gives the virus an advantage in that only a smaller part of it's dna needs to mutate to evade a specific vaccine. Obviously they could have created a vaccine that targets more than one part of the spike, perhaps that will come later after this trial run effectively.