After developing great weakness after both Pfizer booster shots; severe reactions to his 1st and 2nd booster; would fall over like he had no muscle control; This is a spontaneous report received from contactable reporter(s) (Consumer or other non HCP) from medical information team.  An 83-year-old male patient received BNT162b2 (BNT162B2), on 31Mar2022 as dose 4 (booster), single (Lot number: FJ9943) at the age of 83 years for covid-19 immunisation. The patient's relevant medical history included: "Diabetes" (unspecified if ongoing); "heart trouble" (unspecified if ongoing). The patient took concomitant medications. Vaccination history included: BNT162b2 (First Dose: 14Jan2021 NDC, LOT, EXP: Unknown), administration date: 14Jan2021, when the patient was 82-year-old, for COVID-19 immunization, reaction(s): "sore arm"; BNT162b2 (Second Dose: 04Feb2021 NDC, LOT, EXP: Unknown), administration date: 04Feb2021, when the patient was 82-year-old, for COVID-19 immunization, reaction(s): "sore arm"; BNT162b2 (First Booster: 16Oct2021 LOT: FF2589 NDC, EXP: Unknown., Patient became very weak on 17Oct2021 after his 1st booster), administration date: 16Oct2021, when the patient was 83-year-old, for COVID-19 immunization, reaction(s): "weakness"; Bnt162b2 (fell), for COVID-19 immunization, reaction(s): "Fall"; Bnt162b2 (couldn't walk a straight line), for COVID-19 immunization, reaction(s): "Gait disturbance"; Bnt162b2 (BP dropped), for COVID-19 immunization, reaction(s): "Blood pressure decreased"; Bnt162b2 (Patient was found to have UTI and was treated for it), for COVID-19 immunization, reaction(s): "Urinary infection"; Bnt162b2 (Patient could barely get up from the chair.), for COVID-19 immunization, reaction(s): "Activities of daily living impaired"; Bnt162b2 (hit his head), for COVID-19 immunization, reaction(s): "Headache"; Bnt162b2 (Patient's head was checked and had a superficial cut), for COVID-19 immunization, reaction(s): "Skin laceration". The following information was reported: ASTHENIA (non-serious), outcome "unknown", described as "After developing great weakness after both Pfizer booster shots"; MUSCULAR WEAKNESS (non-serious), outcome "unknown", described as "would fall over like he had no muscle control"; IMMUNISATION REACTION (non-serious), outcome "unknown", described as "severe reactions to his 1st and 2nd booster". Relevant laboratory tests and procedures are available in the appropriate section.  Additional information: Patient reported developing great weakness after the both Pfizer booster shots and was enquired if it would be same with the current booster or the ingredients are different. Caller stated that the patient had the Pfizer COVID-19 Vaccine for his primary series and 1st and 2nd booster doses. Patient was fine with the primary series. Patient wanted to get his 3rd booster but had severe reactions to his 1st and 2nd booster. Patient became very weak after his 1st booster. During the patient's 2nd booster, when he sat on the side of the bed, he would fall over like he had no muscle control. Patient was very weak for about two days. Caller mentioned that they had spoken to the primary care doctor who told them to wait if anyone has any type of reaction with the Pfizer COVID-19 Vaccine Bivalent Booster. Caller stated that they were wondering if there were any changes other than the variants with the new bivalent booster to encourage them to take the booster. No other conditions and investigations reported. Patient wrote a letter to Pfizer and received number they gave him. He has had a rather severe reaction to the last 2 boosters of the Covid-19 vaccine. With the original 2 vaccines, the injections, really had nothing more than usual. They were all Pfizer. Had the usual sore arm and nothing else. With the last 2, he had a really severe reaction and became extremely weak. Would like to take the latest, third booster with the new variant and asked if it is made up of the same ingredients as the other vaccines. He was trying to make up his mid, whether to take vaccine or not. Caller passed phone to her husband, the patient. Clarified with the patient, his full name as (withheld) who's details were entered in formal field as reporter and provided remaining details for report. Clarified with patient that he was asking about the ingredients of the latest Covid booster for the new variant. Knows he has to make his own mind up but wanted to find out what information there was. Clarified that patient got number from Pfizer, previously provided online on Pfizer website. Clarified that he did not report anything but had asked question about the ingredients and was told to call. The patient does not remember the treatment details. After the second booster, it was about the same. Didn't fall down but if he was sitting up, he would just fall over, he was so weak. Clarified that he did not go to hospital the second time and this reaction occurred after first and second booster of Covid vaccine. Did not have any real problems with first 2, original doses Covid vaccine. Clarified that patient had 4 total doses Pfizer Covid-19 vaccine, including 2 original doses and 2 booster doses. Concomitant Products/Medical Conditions: Has got several medical conditions and is on gobs of medicine. No additional vaccines administered on same date of the Pfizer suspect. No prior vaccinations, No family medical history relevant to AE and no relevant tests reported.; Sender's Comments: Linked Report(s) : US-PFIZER INC-202201240238 Same patient, drug, and event separated in time;