Has creating worse variants with a vaccine happened with a virus in the past? I think I've heard this theory with bacteria, where we could potentially kill off the ones susceptible to anti-biotics and then only the non-susceptible ones would be left to reproduce, and antibiotics would no longer work, (although antibiotics still work so not sure if this theory is still held) but I couldn't think of a virus where this similar argument was made. My general understanding of viruses is that as time goes on, the new variants will be less deadly. Kind of like everything really, time causes things to break down and fail, short of work being put into them. I would think as new variants come out, they will be less of a concern than the previous variant, short of a virology lab releasing a variant they engineered of course.