Most of the people I know who've had their second shots have had just the swollen/sore arm deal (we had a bit more tiredness and achiness than round 1), except for George. He's the exception so far in my experience.
I have a good friend who ended up in the hospital for a few days, although he was fine a few days after that.
The folks who got it really bad from our lab all got Moderna. Most took a day off even for Pfizer though. But all the vomiting and high fevers came from Moderna.
I just had a sore arm and minor headache/shoulder aches (the latter I am prone to though) after my second (Pfizer) shot.
Becks, do you know if there is any understanding as to why folks react differently to the vaccine? One thought I had was how exposed you are as an adult to groups of sick kids with other (previous) coronaviruses influencing your immune response.
Not that I'm aware of. Everyone who had a super strong reaction in our lab was under 30 - I think there's a reasonable chance that their younger immune systems are probably just over-reacting. It wouldn't surprise me if we were able to back off the dose in these shots a little with optimization in future - you can see that if you were wanting to get a result as rapidly as possible, you'd dial it up to ensure you see a response. But there's probably a lower dose than that that still gives you a strong immune response without this strong reaction.
It could also just be a super efficient delivery mechanism - I've not read anything about it, but I haven't been seeking it out either.