Howdy….my wife ( has allergic reaction tendencies) took the pfizer vaccine for both injections. She had quite severe leg pain and back of neck pain for 1.5 days post injection. A month later she had a colonoscopy and the same reaction occurred. In looking at the ingredients of the Pfizer vaccine and the colonoscopy prep kit the only common ingredient is PEG or Polyethylene Glycol. it Would seem that PEG just might be the culprit. That said, the J&J vaccine has no PEG as an ingredient. My question….can you mix your vaccine…meaning….can you substitute J&J for Pfizer for your “ Booster” to try to avoid the former reaction ? She will be traveling internationally in February and would like the Booster if possible. I have a call into her Doc….and waiting for a call back for an answer . Thought I would check with the Board as well for any similar reactions etc….Thanks !