My daughter-in-law (age 40) is an ER doc and got both Pfizer shots. No reaction to the first one but felt lousy for a day or so after the second. She says she doesn't know anyone who hasn't had at least some reaction to the second shot.
My wife and I (age 70+) got the first Moderna. Sore arms but nothing more. She gets the second shot next week. I can't get my second one scheduled because the website crashed in a couple of minutes when the local government announced that spots were available for second Modernas ( apparently I don't type quite fast enough to outrun the crash). I guess I get an opportunity some time next week to test my typing speed again.
I've read that people 65+ don't have as pronounced a reaction to the second shot because older people don't have as good an immune system function as younger people. True ? I have no idea.