Each person's metabolism and body adaptation is different. I've been getting the two shots together for several years...

True. But it does make sense to have your immune system tackle one vaccine at a time, and then recover. I also have been getting them at the same time, in part because "just get it over with", and it's more efficient to take care of all shots on one trip. I did RSV along with the others a few years ago, all at once (2023, as I recall).

But my immune system is pretty aggressive. The flu shot leaves me a little tired and achy. But the COVID shot puts me down. Fever, chills, fatigue. It's like I have COVID. Lasts about 48 hours, and it's over.

I figure my immune system is learning to fight the bug, so I tolerate the side effects with the knowledge that I either a) won't get it, or b) will get a very minor case of it. So far it's been true. I've had COVID at least twice, and it was no worse than a nasty cold because I was vaccinated. I knew people that died without the vaccine (one younger than me).