So, I’ve heard mixed thoughts depending on the type and cause of immune compromise. I have had some friends who have more significant, not well controlled autoimmune issues (like lupus, RA, MS) have a flare up after the booster. They also have had a less protective response to the shot if they had to take steroids to control the immune flare while getting the booster.
In my case, I am immune deficient (low/no antibodies, low t cells, and some GI autoimmune dysfunction mixed in for good measure). Most of us in that category were able to get boosters without any significant flare or complication. My GI has been flaring for weeks and that was before a booster, so the booster didn’t really affect my flare up.
Personally, I am never 100% and if I waited for that day, I would never get a booster…so I just did it when I knew my schedule was a bit less crazy, so that I could have a week or 2 if I needed extra time to recover. My second shot was actually worse than the 3rd shot…I had a few punky days, but nothing major. Honestly, I was more worried about getting the booster to try and get what little protection I could…I’m use to dealing with my crappy feeling body on a daily basis! But that’s just my personal perspective…and I know that things like vaccines are not going to trigger more of a flare for me. If you know that vaccines usually do cause a worse flare, then I could see a different approach.