I got my Pfizer booster 3 weeks ago, flu shot yesterday, no more than a little sore arm..
My wife got her flu shot 3 weeks back, was waiting on the Moderna booster, had an appointment yesterday but when she got there, they said they didn't have the right needles.. So she rescheduled for next week, same pharmacy (Safeway/Von/Albertson) that I've used for flu shots for years, and the Pfizer booster a while back. I asked when I was in for the flu shot of they were doing Moderna, she said they began the evening before...
So supplies, even needles matter, apparently... I was surprised that there was a different needle for the Moderna.. She had a rough reaction to the 2nd Moderna, so it will be interesting to see how the booster goes...