I feel that both this and EYs complex nanotechnology are far too fairy tale like.
Any competent virologist could make a vaccine resistant, contagious, highly lethal to humans virus. We know how to do it - this is the entire field of gain of function research. It doesn't need any global infrastructure - just a local lab, resources at the few million dollar level, and intention. An AGI could certainly do this. No new technology (beyond the AGI itself) required. I feel that if any scenario is going to convince the "no problem here" skeptics it would be that one. Especially since COVID is a highly contagious, new virus that by dumb luck is not all that lethal.