The efficacy rates among the vaccines aren’t direct comparisons though. The Pfizer and Moderna ~95% efficacy rates are derived from their tests/trials that were done early on in the pandemic. J&J ran their trials later and in different countries, when there were already mutated strains out in the wild.
There are side effects to be sure with the mRNA ones as well. Myocarditis/heart inflammation for young men for instance. I’m of the opinion that the mRNA vaccine side-effects are being kept a little more quiet than J&J, and one day the dam will break with people coming forward. They’re more experimental and the J&J is a more traditional vaccine. That’s enough of an incentive for a lot of people who want the vax but are leery of being too much of a guinea pig.
FWIW, anecdotally, my buddy’s older sister got the Moderna and had a mild stroke within the week. She’s about 50 and was in otherwise very good health. She’s a hardcore lib and really big on the vaccines, so she tried to keep it quiet, and didn’t want to call attention to it.