diarrheal discharge of both goop and intestinal matter; This is a spontaneous report received from contactable reporter(s) (Consumer or other non HCP). The reporter is the patient.  A 78 year-old male patient received bnt162b2 (BNT162B2), administration date 15Oct2021 (Lot number: EW0169, Expiration Date: 30Nov2021) at the age of 78 years as dose 3 (booster), single for covid-19 immunisation. Relevant medical history included: "Thyroid disorder" (unspecified if ongoing), notes: long term thyroid disorder; "Mononucleosis" (unspecified if ongoing), notes: It is Mononucleosis that did not go away.; "All muscles got stiff" (unspecified if ongoing), notes: All muscles got stiff for a couple of days, after the flu shot.  It was discomforting.; "discomforting." (unspecified if ongoing), notes: All muscles got stiff for a couple of days, after the flu shot.  It was discomforting. Concomitant medication(s) included: FLU, administration date Oct2021. Vaccination history included: Bnt162b2 (DOSE: 1, Batch/lot number: EW0169, Expiry date: 30Nov2021), administration date: 02Feb2021, when the patient was 77 years old, for COVID-19 immunization; Bnt162b2 (DOSE: 2, Lot number: EL9267, Expiry: 31May2021), administration date: 31May2021, when the patient was 78 years old, for COVID-19 immunization.  The following information was reported: DIARRHOEA (non-serious) with onset Oct2021, outcome "recovering", described as "diarrheal discharge of both goop and intestinal matter". The event "diarrheal discharge of both goop and intestinal matter" was evaluated at the physician office visit. The patient underwent the following laboratory tests and procedures: sars-cov-2 test: (19Oct2021) unknown result, notes: Nasal test. Therapeutic measures were taken as a result of diarrhoea. No follow-up attempts are possible. No further information is expected.   Additional information: This past Friday afternoon and received booster shot for COVID vaccine. Within less than 24 hours he started to experience diarrheal discharge of both goop and intestinal matter. It continued for about a day and a half maybe two. One was to drink Gatorade and he did that and to eat bland stuff. The diarrhea, at least temporarily was discontinuing. The doctors office said to take a container with the stuff to the local clinic in (withheld). He did that this morning. They were not interested and sent him to get COVID tested and he did that. Now they tell him that he would be informed after a couple of days. He was not scheduled for an appointment with a physician today. He did not know if this is over yet. It was not very pleasant. He tried to call VAERS and the only thing they were good for sending him a form to fill out. Caller has no indication it has been reported including at the clinic. He talked with a nurse and got COVID test. It has tapered off after he drank Gatorade and did not eat very much. He has only had a couple of ripe bananas and toast over 24 hour period. And Gatorade that has no sugar. He took a couple Ricola candies and those went down ok. Prior to that he was drinking water and had cut down on medication and practically everything else. Finally he stopped passing whatever. Initially it was coming out like chocolatey goop. Then the very last one occurred last night. After most of it had dissipated, it was a couple of farts and couple of blood drops. He did not notice blood in prior discharges. It got all over everything. Once it was going to come it was going to come. It was not pleasant. From what has been said to him continuing and disabling diarrhea was not associated with booster shot yet. That was what he has heard. Loss of fluid has been pointed out to him several times as a dangerous situation. It has tapered off after he drank Gatorade and did not eat very much.   Description of complaint: Caller reporting adverse event with booster shot for COVID vaccine. The reason he got it was because the first and second shot seemed to be very settling for him. With limited medical background, his impression is either the first or second may have settled and activated the immune system with the other viral complications which were documented over the years. That is a wild guess. He w  as very surprised there was a reaction to this. It could be an over reaction of immune system. They sent him to get COVID nasal test. In 2 days he will get the results. If for some reason he has acquired disimmunity there will be more questions.    No follow-up attempts are possible. No further information is expected.