Erythema on his upper back/extended to his buttocks, thighs and legs; Biopsy skin consistent with allergic reaction; Itch on his upper back/extended to his buttocks, thighs and legs; Urticaria on his upper back/extended to his buttocks, thighs and legs; Some spots that open up and come back on his upper arm, axilla, parts of his back; This spontaneous case was received on 14-Sep-2021 from physician (anesthesiologist) (reference number: 202101127869), with additional information (being processed together) received on the same day (reference numbers: SEQW21-02231 and SEQW21-02242) and concerned a 62-year-old, male patient.   The patient's concurrent conditions included osteoarthritis (since 2001), acid reflux/gastrooesophageal reflux disease (GERD) and penicillin allergy, developed when he was 12 years old. The patient's concomitant medications included Aspirin (acetylsalicylic acid) for stroke prevention, Pepcid (famotidine) and Zegerid (omeprazole) (reported as over the counter Prilosec (omeprazole) plus bicarbonate), both for antireflux/heartburn, vitamin B12 (cyanocobalamin), vitamin D3 (colecalciferol), multivitamin (unspecified vitamins), Lutein (xantofyl), Omega-3 (docosahexaenoic acid, eicosapentaenoic acid), Osteo bi-flex (chondroitin sulfate, glucosamine hydrochloride) and Red Yeast Rice tablets (monascus purpureus), all used for an unreported indication. The patient had a planned elective shoulder replacement surgery on 02-Aug-2021. The patient's historical drug included penicillin, at the age of twelve when it caused a non-significant rash. The patient had taken cephalosporins with no problems and Ancef (cefazolin) which patient took before his shoulder surgery. On 19-Dec-2020 and 09-Jan-2021 the patient was vaccinated with first dose and second dose of non-company Pfizer Biontech COVID-19 vaccine (COVID-19 mRNA vaccine) to prevent getting COVID.   On 17-Aug-2021, eight months after the patient's last shot, the patient was vaccinated with third dose of non-company, co-suspect Pfizer Biontech COVID-19 vaccine (COVID-19 mRNA vaccine; anatomical location: left upper arm, dose and route of administration: not reported) to prevent getting COVID. The batch number reported was FC3181.   On the same day, the patient was vaccinated with Afluria Quadrivalent (influenza vaccine; dose, route of administration and anatomical location: not reported) to prevent the flu. The batch number reported was P100344370.   On 18-Aug-2021, when he woke up the next day at 7 am, the patient experienced severe itch, erythema and urticaria on his upper back. The patient stated that over the next 24 hours (also reported as 48 hours) it extended to his buttocks, thighs and legs. The patient spoke to the dermatologist but was not taken seriously at first, so he also took pictures. The dermatologist thought it could be contact dermatitis.   On 20-Aug-2021, reported as Friday, the patient went to see the dermatologist and the doctor thought it could be many things. The patient was given high dose steroids, prednisone taper, Zyrtec (cetirizine hydrochloride), Benadryl (diphenhydramine hydrochloride) and clobetasol. On the same date, the dermatologist took a biopsy and results were consistent with allergic reaction.   On an unspecified date in Aug-2021, reported as Saturday, the patient tapered down his prednisone dose and finished the treatment.   On an unspecified date in Aug-2021, the patient developed some spots that opened up and came back on his upper arm, axilla and different parts of his back. The patient stated his dermatologist could not offer anything else to him. The patient visited an allergist, but doctor did not know what caused this. He was still taking antihistamines as the lesions started to show up.    At the time of initial reporting, the patient was recovering from all the events as they improved significantly with steroids, except for 'spot-like rash'. The patient stated that treatment medications had some good effect. The patient had not recovered from the event of 'spot-like rash' and he was still taking antihistamines.    The reporter assessed the events as possibly related to Afluria Quadrivalent. The reporter stated he could not say if it was from the vaccine with certainty, but timing of events led him to believe it was the COVID-19 or flu vaccine. He took them together and nothing else had changed.   The reporter assessed all events as serious due to seriousness criteria of medical significance and disability.  Company comment: A 62-year-old patient was vaccinated with Afluria Quadrivalent. One the same date, the patient was vaccinated with third dose of non-company, co-suspect COVID-19 vaccine.  One day later, the patient experienced severe itch, erythema and urticaria on his upper back. It extended to his buttocks, thighs and legs. Two days later, the patient went to see the dermatologist. The doctor took a biopsy and results were consistent with allergic reaction. Causality was highly confounded by co-suspect COVID-19 vaccine. However, causal role of the suspect vaccine is assessed as possibly related, considering biological and chronological plausibility.; Reporter's Comments: The reporter assessed the events as possibly related to Alfuria Quadrivalent. The reporter stated he could not say if it was from the vaccine with certainty, but timing of events lead him to believe it was the COVID-19 or Flu vaccine. He took them together and nothing else had changed.; Sender's Comments: A 62-year-old patient was vaccinated with Afluria Quadrivalent. One the same date, the patient was vaccinated with third dose of non-company, co-suspect COVID-19 vaccine.  One day later, the patient experienced severe itch, erythema and urticaria on his upper back. It extended to his buttocks, thighs and legs. Two days later, the patient went to see the dermatologist. The doctor took a biopsy and results were consistent with allergic reaction. Causality was highly confounded by co-suspect COVID-19 vaccine. However, causal role of the suspect vaccine is assessed as possibly related, considering biological and chronological plausibility.