I think they're meeting in the middle and the pain cancels out!!
(just kidding- never have had pain from a flu vax, and the first two rna vax shots didn't give me anything that I could legitimately call a side effect either. Currently just waiting to overcome laziness to schedule the booster).
booster scheduled next friday (to avoid potential interference with work). The mrs got hers (pfizer) yesterday as she's health care. I'm 205 pounds which is just over the threshold to get early access for high risk, otherwise I'd have to wait (initial second shot 8 months ago, too). The mrs. had a bad reaction to the original second shot and was in bed for a day and a half, I had nothing.
So far today, she's up saying nothing more than some minor soreness in her chest (she's not tubby like me).
Had my booster last Sunday. I'm in the high risk category and I was waiting for information from my GP surgery but nothing happened and as the six month period had expired I looked up the NHS website and found a walk in centre about 14 miles from me. That only took about a good twenty minute drive across rural roads so not much of an inconvenience.
I got there are 9.00am only to be told it didn't start until 10.00 which was contrary to the website info but they gave me a form to fill in and when they opened I was straight in without any wait.
They also gave me the influenza vaccine at the same time so 'm like my cats, all up to date with my vacs.
As normal, no side effects for me as such but the following day my arm ached really badly where the booster had been injected and felt like I'd ben kicked but it was only for about 24-36 hours and nothing else and no other side effects after that.