I've been taking D, C, Zinc, Quercetin and NAC for a year and upped the dosages when I started feeling symptoms. It's all been mild throughout but it's definitely taking a week+ to run its course. Started with a couple days of mild chills/ temp around101, then moved into a couple/few days of mild sore throat and dry cough. Then a few days of general stuffiness and loss of taste and smell. If I didn't know, I'd just say it's a cold like colds I've had in the past that always lingered at least a week before being 100% back to normal.