I'm of the opinion that COVID infections as well as vaccination could contribute to this. My options were to vaccinate or face COVID without being vaccinated. Based on my experiences, I chose to get vaccinated. This was when the vaccines were 90%+ effective, prior to mutations that made them far less so. I got one booster, as Omicron was coming over, but have not pursued further vaccination, and won't unless COVID cases kick up in greater numbers, and/or a more effective vaccine comes out for the strains involved. I chose Pfizer because of its efficacy being similar to Moderna, with a much lower effect on the recipient. I never considered J&J, as it was far less effective and had more side effects from the literature I read. I think people went with it because of cost/1 and done (interestingly, the 1 and done J&J was similarly effective to half the Prizer/Moderna series, so you COULD have just done that...), and because of fear of newer methods/mRNA vaccines.