Colds are supposedly caused by bacteria. The flu (in all its variations) is a virus. When I was in the military, the mantra was, “sweat it out!” which is both right and wrong.
If you have recovered from a cold, go to yoga! If you have a virus, or the flu, stay away.
Once you get a cold, you’ve got it – your body fights it and exertion may help that.
But a virus thrives in warm temperatures. Make your body hotter, in a hot room, and that illness you thought you overcame may come back in spades, because you gave it such a wonderful environment to grow in.
Check with your doctor. I am not a doctor, but have experience in this area. Plus personal experience on this topic has held this line of reasoning to be true.
Hope this helps…