Severe allergic reaction/ Started with an allergy it was really bad; She received the first two doses of COVID-19 vaccination from Moderna vaccine, and then received a third dose on 04Nov2021 from Pfizer COVID-19 vaccine; Booster; Had a rash near the buttocks/started in the middle of my back; Rash, it goes away and that's it. The following days it started in the middle of my back, lasted almost two weeks with an exasperating itch; Couldn't go to work; The inflammation in the skin was absurd; Skin is all red; It completely broke out all over my body, I got an impressive rash; Started with an allergy it was really bad/ It was very irritating and the itchiness was incredible; Started with an allergy it was really bad/ It was very irritating and the itchiness was incredible; This is a spontaneous report received from contactable reporter(s) (Consumer or other non HCP) from medical information team. The reporter is the patient.  A 50 year-old female patient received bnt162b2 (BNT162B2), administered in arm left, administration date 14Nov2021 (Lot number: 30145BA) at the age of 50 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: Covid-19 vaccination (Dose: 1, COVID-19 vaccination from Moderna vaccine), for COVID-19 Immunization; Covid-19 vaccination (Dose: 2, COVID-19 vaccination from Moderna vaccine), for COVID-19 Immunization. The following information was reported: INTERCHANGE OF VACCINE PRODUCTS (non-serious) with onset 14Nov2021, outcome "unknown", described as "She received the first two doses of COVID-19 vaccination from Moderna vaccine, and then received a third dose on 04Nov2021 from Pfizer COVID-19 vaccine"; IMMUNISATION (non-serious) with onset 14Nov2021, outcome "unknown", described as "Booster"; RASH (non-serious) with onset 2021, outcome "recovered" (2021), described as "Had a rash near the buttocks/started in the middle of my back"; RASH PRURITIC (non-serious) with onset 2021, outcome "unknown", described as "Rash, it goes away and that's it. The following days it started in the middle of my back, lasted almost two weeks with an exasperating itch"; IMPAIRED WORK ABILITY (non-serious) with onset 2021, outcome "unknown", described as "Couldn't go to work"; INFLAMMATION (non-serious) with onset 2021, outcome "unknown", described as "The inflammation in the skin was absurd"; ERYTHEMA (non-serious) with onset 2021, outcome "unknown", described as "Skin is all red"; RASH (non-serious) with onset 2021, outcome "unknown", described as "It completely broke out all over my body, I got an impressive rash"; HYPERSENSITIVITY (non-serious) with onset 16Nov2021, outcome "recovering", described as "Severe allergic reaction/ Started with an allergy it was really bad"; SKIN IRRITATION (non-serious), PRURITUS (non-serious) all with onset 2021, outcome "recovering" and all described as "Started with an allergy it was really bad/ It was very irritating and the itchiness was incredible". The event "skin is all red" was evaluated at the physician office visit. Relevant laboratory tests and procedures are available in the appropriate section. Therapeutic measures were taken as a result of rash, inflammation, rash, hypersensitivity, skin irritation, pruritus.  Additional Information: The patient stated that, it started with an allergy it was really bad and started slowly and started to get worse and worse. It was all over her body and arms and face and stomach and back and legs and everywhere. It was very irritating, and the itchiness was incredible. This reaction started on 16Nov2021, and the caller had an appointment at work, and she had to go home because it was so bad. Right now, the caller is better, but she has been taking medicine for 2 days. Right now, the caller is taking corticoids. The caller started with normal allergy medicine but now she is on 40 mg of Prednisone and has to take it for 3 days, she has to take 40 tablets, then the next 3 day she has to take 30 tablets and keep going on until they're finished. The caller is also taking and anti-allergic medication Zyrtec 10 mg and Hydroxyzine HCL 10 mg that she has to take before bed.  No follow-up attempts are needed. No further information is expected.