Could I get some more context on this or a direction to start researching?
I feel this would be great information to share with the vax hesitate crowd. I have heard a few people say the vaccines are too new and not tested enough.
Also, replying to the grandparent: vaccines per se are not necessarily safe out of the door, they're medical products and as such can have potentially many unforseen and troubling consequences. However, in the past all the unforseen consequences of any vaccine (whether still used, or since then retracted from the market due to problems) would become known a few months and a few tens of million people into the phase 3. That's when it is very, very safe to jump on board. And this is definitely already the case with all the popular covid vaccines.
To summarize: human data trumps everything in medicine, and we've had A LOT of data points.