arm swelling; a little bit of a fever; rash; immunocompromised received his booster dose on 1Sep2021; immunocompromised received his booster dose on 1Sep2021; administered his booster shot into the triceps muscle and they administered it subcutaneously; joint pain; This is a spontaneous report from a contactable nurse via Pfizer-sponsored program. A nurse (wife) reported for (husband) 39-year-old male patient that: A 39-year-old male patient received third (booster) dose of BNT162B2 (COMIRNATY, Formulation: Solution for injection, Batch/Lot Number: Either EW0171 or EWO171, Expiry date: Unknown), via subcutaneous route of administration on 01Sep2021 at 10:30 (at the age of 39-year-old) as DOSE 3, SINGLE for covid-19 immunisation. Medical history included immunocompromised from an unknown date. Concomitant medication includes taking biologic. Historical vaccine included first dose of BNT162B2 (COMIRNATY, Formulation: Solution for injection, Batch/Lot Number: EH9899, Expiry date: Unknown), via unspecified route of administration on 21Dec2020 (at the age of 38 year old) as single dose for covid-19 immunisation and experienced sore arm and second dose of BNT162B2 (COMIRNATY, Formulation: Solution for injection, Batch/Lot Number: Either EL3246 or EL324G, Expiry date: Unknown), via unspecified route of administration on 12Jan2021 (at the age of 38 year old) as single dose for covid-19 immunisation and experienced sore arm. Patient's wife reported behalf of patient (husband), It was reported that immunocompromised received his booster dose on 01Sep2021, developed arm swelling, swelling didn't start until last night, 02Sep2021, that is not her concern necessarily. She is concerned because she believes that the vaccine was administered subcutaneously instead of intramuscularly and that it was administered by the triceps instead of the deltoid. Dates for experienced arm swelling with the booster shot and he also has had the same symptoms that he had with the last two doses of the Pfizer COVID vaccines was on 02Sep2021. She says that for the symptoms that her husband experienced with the first 2 doses she didn't see swelling around his arm, but he said that he had some arm soreness on the first 2. It started the next day and it was not as late. The only thing that is a different side effect is that he had joint pain with this dose, within minutes beginning on 01Sep2021 and he hasn't complained anymore about it so she thinks it may be gone, the joint pain yesterday just mainly his arm being in pain, and he had a rash and a little bit of a fever, but nothing too serious. Reporter also stated that the band aid was lower and off to the back of his arm. It looks like administered in the triceps and not in the deltoid. A lot of the symptoms that he had usually with the other ones came a little bit sooner but yesterday it had come around, 7:00. Reporter stated he was still experiencing but it was not bad enough to take him to the emergency room or anything like that. Reporter queried that Should he be reposed with the booster vaccine if it was given subcutaneously or by the wrong muscle. The ACIP notes that if an authorized COVID-19 Vaccine is administered via the incorrect route (e.g., subcutaneous) or at the incorrect site (i.e., site other than the deltoid muscle [preferred site] or anterolateral thigh [alternate site]), do not repeat the dose. Inform the recipient of the potential for local and systemic adverse events.3 If the dose given in error is the first dose, a second dose should be administered at the recommended interval (21 days [Pfizer-BioNTech] or 28 days [Moderna]). If this dose is the second dose, the series is complete, and no additional doses are needed. Please note that Pfizer is independent of these recommendations. Reporter learned that a vaccine injected into the fat may metabolize differently and he might not get the same B and T cell response. Reporter also queried was there any antibody test or titer that could be checked to see if he had appropriate immunity and should he receive an additional dose besides the booster. Antibody testing is not recommended to assess for immunity to SARS-CoV-2 following COVID-19 vaccination because the clinical utility of post-vaccination testing has not been established. With regards to COVID-19 vaccine immune response and effectiveness in moderately and severely immunocompromised people the following is mentioned:2 The utility of serologic testing or cellular immune testing to assess immune response to vaccination and guide clinical care (e.g., as part of need assessment for an additional dose) has not been established. Serologic testing or cellular immune testing outside of the context of research studies is not recommended at this time. The additional mRNA COVID-19 vaccine dose should be the same vaccine product as the initial 2-dose mRNA COVID-19 primary vaccine series (Pfizer-BioNTech or Moderna). If the mRNA COVID-19 vaccine product given for the first two doses is not available, the other mRNA COVID-19 vaccine product may be administered. A person should not receive more than three mRNA COVID-19 vaccine doses. Caller reporting AE/ MI following her husband receiving the booster dose of the COVID vaccine and mentioned that he is taking biologics and if he unfortunately got COVID 3 months down the road she doesn't want the vaccine to not be effective and have to take him to the hospital because it was administered into the triceps muscle instead of the deltoid and they administered it subcutaneously instead of intramuscular. Seriousness: It is not life threatening she doesn't think and. As far as the side effects being serious, it would just be serious if it wasn't given correctly because of the importance of the vaccine and everything that is happening right now with the delta variant then maybe it would be more serious. Outcome of the event arm swelling was not recovered and rest all were unknown..  Causality: Yes, because all of the side effects are the same ones he got with the first two doses, there was nothing major just the sore arm but that may be because it was administered into a more tender site.   The lot number for the vaccine, [BNT162B2], was not provided and will be requested during follow up.