[e_y_]

It's probably too early to say if the vaccines have had any effect on the mutation rate, since wide-scale vaccination has only just started ramping up.

You'd think it'd be easier to say whether people are getting reinfected after catching COVID the first time, but the testing data is sparse enough that there doesn't seem to be any confirmation on whether it's widespread or just isolated cases. Most notably in Manaus, Brazil, where one of the new variants has been spreading.

I'm definitely not qualified to make anything other than wild guesses on this subject, but everything I've read suggests that scientists are scratching their heads as well. Conventional wisdom is that the spike is the easiest to target, so whether the human immune system picking the N protein is a mistake or brilliant move seems to be up in the air. Some reading: https://www.nature.com/articles/s41577-020-00480-0

Mutating to a less severe variant: Given that SARS-CoV-2 already has delayed symptoms and a high percentage being asymptomatic cases, I'm not sure there's much pressure to make it milder. Also the overall spike design is what gives SARS-CoV-2 its higher infectiousness compared to the original SARS, so one would hope that mutations to it (to avoid existing antibodies) would tend to make things less effective, although unluckily the virus has been discovering some new configurations that are both more infectious and also less protected against by the existing vaccines (especially the 60-70% ones). Paper on infectivity of variants: https://www.cell.com/cell/pdf/S0092-8674%2820%2930877-1.pdf