I'm just gonna share this here and leave it up to people as to whether not to believe me, but when I moved to Canada I had gotten a really bad cold. An old lady I worked with asked me if I had ever taken Echenacia. Hadn't heard of it. She said to start taking it at the first sign of cold symptoms and continue 3x daily like an antibiotic until the symptoms have cleared. No joke, every cold I've had since then (2017) has only lasted 4 days or less, and the symptoms are very manageable and mild.
It's honestly the single most effective supplement I've ever entertained, and it's relatively inexpensive to pick up in any pharmacy or supplement aisle.