This recipe is from Herbs Gone Wild by Diane Kidman via Sandy Barrett. This sounds similar to the other recipe that I have but it adds alcohol which would definitely make it last longer.
1 c Elderberries
Place Elderberries in a pan and smash them well.
Simmer on very low heat and continue to smash so you can release as much juice as possible.
Once you've released the juice, strain out the crushed berry material and measure the juice.
Add an equal amount of Honey to the juice along with
pinch of Cinnamon, Clove or Ginger to your taste
Add a few drops of lemon and
20% alcohol (vodka works well)
For instance, if you have 10 ounces of juice, you'd want to add 2 ounces of alcohol.
You can take this syrup liberally as soon as you feel the symptoms of cold or flu sneaking up.
Take it often.
This is one time you won't mind taking your medicine.