What was stated before jibes with what I've read before, that those who have autoimmune disease do NOT want to "boost" the immune system, since it is an overactive immune system that caused the problems in the first place. That said, You'd have to buy into the notion that echinacea supplements would actually do what you'd hope they would do, namely "boost the immune system." There is not much evidence in that regard. So, not likely to help or hurt (except maybe your wallet).
https://nccih.nih.gov/health/echinacea/ataglance.htm
Jan