Here's my experience:
On the day I first feel the beginning of a cold/flu:
I take a bite or 2 of Garlic Chives. They are mild and easy to use.
And when chewed up at the first signs of a cold, they usually stop it quick.
They help later on in the course of colds and flus.
Simply eat a bit of the green stems & flowers too.

The plants can take cold too.
I once was sick and used garlic cloves. Hot to taste, and to make them work, I had to take so much
I reeked of garlic.

The cloves are mild and don't make me stink, and they work fast.
Can order starts on computer system.
Some nurserys carry it too.