I know this sounds trivial, but there's data that suggests common immune-systems boosters such as zinc and vitamin C do help with covid-19.
https://journals.plos.org/plospathogens/article?id=10.1371/j...
https://journals.plos.org/plospathogens/article?id=10.1371/j...
Zinc supplementation may of course help if you are deficient, but the study can't really tell if 'healthy' Zn2+ concentrations contribute anything to the inhibition of viral replication.
It can be normal, over-active, under-active, and likely both. "working or not" is too simplistic for this discussion.
> A 'boosted' / over-active immune system results in auto-immune diseases like Crohn's (which is what I have).
Yes, but that doesn't mean that a temporary boost couldn't potentially help in certain situations.
Along those lines, I bet if you really needed a specific live vaccine your doctor would have you suspend that drug for a little bit.