I am not totally sure if this really helps in soothing cough or flu; but it does make a good and refreshing drink for myself!
To make it: soak the lemons in 3:1 ratio of water: vinegar for 30 minutes. Boil the lemon in vinegar water for a minute. Scoop the lemon out and cool them in room temperature water. And then slice the lemon. Place them into a jar. And fill it up with honey. Put it overnight (in fridge) for a night. Take a lemon or two out each time and add water (plus ice)! Yums!