Diarrhea; back pain; This is a spontaneous report from a contactable consumer (patient). A 78 year female patient received 2nd dose of BNT162B2 (PFIZER-BIONTECH COVID-19 VACCINE, Lot: ER2613) at single dose via an unknown route in right arm on 27Mar2021 for Covid-19 immunization. Medical history included autoimmune system hepatitis, High Blood Pressure, Lung Cancer in remission. She further stated that she had surgery in the past that messed up her liver and kidneys, her autoimmune system went wacky. She had diabetes previously, but no longer had that.  No family Medical History Relevant to the event. Concomitant drugs included ongoing metoprolol succinate ER 50mg tablet orally once daily for high blood pressure (patient had been taking 20 years as of 06Apr2021 if not longer), ongoing apixaban (ELIQUIS) 2.5mg tablet orally at 2.5 mg twice per day from an unknown date to an unknown date for about 4 or 5 years as of 06Apr2021 for blood clot, and 5 mg twice a day Mar2021 as she developing another blood clot while on the 2.5mg and raised the dose (AER 2021379982), ongoing azathioprine tablet 50 mg tabs orally once daily (been taking it about a year as of 06Apr2021), ongoing spironolactone 25mg tabs orally once daily from 2020, ongoing escitalopram 10 mg tablets orally once daily from an unknown date (reported as started in 2020 or a little bit longer ago), ongoing azathioprine (IMURAN) from 2017 at 50 mg tablets orally once daily for hepatic cirrhosis, and biotin, carbohydrates nos, fats nos, minerals nos, potassium, proteins nos, sodium, vitamins nos (BOOST) drinks for years. Patient stated one of her medications was to help calm her down, but she did not know which one. Historical vaccine included 1st dose of covid-19 vaccine (lot number EN6198) on 06Mar2021 in left arm for Covid-19 immunization (AER 2021379069). She went to the hospital after her first Pfizer COVID-19 Immunization. She explained that she had previous surgery and she was having trouble with a colonoscopy that was done 5-6 years ago. She went in to have a mesh put in to take away the pain. She could not recall if the surgery to have mesh placed was before or after the first Pfizer COVID-19 vaccination. She later added she thinks she had the surgery on 02Mar2021, but she not sure. She confirmed she did not think she had ever had any other Pfizer vaccines. No additional Vaccines Administered on Same Date of the Pfizer Suspect.  No other vaccinations within four weeks prior to the first administration date of the suspect vaccine. Patient had the 2nd dose of the vaccine and since developed diarrhea especially right after she eats. Patient never dawned on her that the vaccine was what was causing this, it came on all of a sudden, she didn't connect the two. Diarrhea started last week as of 06Apr2021, but did not know the exact date, been going on about 4 or 5 days now. Patient had not taking anything for the diarrhea. First she thought it was coming from the BOOST she drinks. She stated did not drink it every day, but most often she did. She had been drinking BOOST for years, and never had diarrhea from it, but she stopped drinking it and the diarrhea continues. It was also reported that "it was It didn't occur to her until night of 05Apr2021" that the Pfizer COVID-19 vaccinations could have been the cause.  She called the doctor about pain in her back and telling the doctor she wasn't sure if it was pain from the surgery or pain from the recent Pfizer COVID-19 immunization. The doctor told him if it got any worse to go to the emergency room, but it got better. Patient stated that it got better and she did not go to the emergency room, and did not go to the hospital. She had recovered from back pain. Outcome of Diarrhea was not resolved.  No Emergency Room/ Physician Office visit due to the event. All her tests have been good, no additional details provided. No Relevant Tests performed.  The report was considered non- serious.      No follow-up attempts are needed. No further information is expected.