I doubt anyone actually knows the answer to this, but also have doubts something like Elderberry would be of benefit for the symptoms caused by the vaccine. I think the best option would be to treat symptoms in this case. Muscle pain - Black Cohosh or possibly Horse Chestnut or Sweet Melilot (see below), headache (depends on the type and location of the headache) - neck pain - Passion Flower or Kudzu, dull, throbbing headache - Horse Chestnut, headache with sharp , stabbing pain - Sweet Melilot, etc, chills ginger or cinnamon