Booster; they thought that it was cellulitis; Allergic reaction; arms became very swollen/ hand swelled up twice the size it was; arm swelled up and his whole hand swelled up, it wasn't just on the injection site; arms developed redness; arms developed itching; This is a spontaneous report received from contactable reporter (consumer) from medical information team.  An 82-year-old male patient received BNT162B2 (PFIZER-BIONTECH COVID-19 VACCINE), administered in arm right, administration date 13Oct2021 (lot number: FC3181) at the age of 82-years as dose 3 (booster), single for COVID-19 immunisation. The patient had no relevant medical history. There were no concomitant medications. Vaccination history included: BNT162B2 (lot number: EL8982, in right arm as dose 1, single), administration date: 21Jan2021, when the patient was 81-years-old, for COVID-19 immunisation, reaction: "side effects did not occur"; BNT162B2 (lot number: EL9267, in left arm as dose 2, single), administration date: 11Feb2021, when the patient was 81-years-old, for COVID-19 immunisation, reactions: "Cellulitis", "redness on the injection arm", "swelling half way down to his wrist on the injection arm", "itching on the injection arm", and "warm to the touch on the injection arm"; Flu shot (for this year's flu shot he got it in his backside), reactions: "No reactions"; and Pneumonia shot. The patient received all three doses of Pfizer COVID vaccine. After the booster dose that he had on 13Oct2021, the patient's arms developed redness, itching, and it became very swollen on Oct2021. It looked like it's going burst. It took about 2 weeks to go away, and they had to go to emergency and multiple doctor's visit. These side effects did not occur after the first dose. Because they didn't know if it's going to happen the third, they didn't know if he was allergic to something in it or if this was something common. They didn't know anybody who had the reaction like this, they didn't know if it was something in the shot that he's allergic too. His arm swelled up and his whole hand swelled up twice the size it was, from his shoulder all the way down to the tips of his fingers. It wasn't just on the injection site; it was from the injection site all the way down to his fingertips. His doctor was in awe on what it looked like. The doctor though it was cellulitis and then they said that they were pretty sure that it was an allergic reaction. No one at the hospital could give him an exact thing of what happened. The reporter doesn't want the patient to get the vaccine again and end up in the hospital again. They have already been to the emergency room twice. He had the booster dose on 13Oct2021 and then he was in the hospital because they went to the emergency room again on 21Oct2021, because his hand was so bad. Before that, the patient had already gone to the doctor's office twice and had changed antibiotics and the doctor's office would put him on one and the hospital would put him on 2 to 3 different ones. The hospital was just as perplexed with what he was experienced, they didn't know what it was. They had released him from the emergency room the second time, the doctors had gotten together and talked, and they were not sure whether it was an infection or a reaction. They were leaning towards it being a reaction. The booster dose was given either at 16:00 in the afternoon or 19:00 in the evening. The events "they thought that it was cellulitis", "allergic reaction", "arms became very swollen/ hand swelled up twice the size it was", "arm swelled up and his whole hand swelled up, it wasn't just on the injection site", "arms developed redness" and "arms developed itching" were evaluated at the physician office visit and emergency room visit. Therapeutic measures were taken as a result of cellulitis, hypersensitivity, peripheral swelling, vaccination site swelling, erythema, and pruritus. The outcome of the event "booster" was unknown and recovered on an unspecified date in 2021 for all other events.