Patient got three doses of COVID vaccine at the same time; Patient got three doses of COVID vaccine at the same time; profound fatigue; body aches/General body pain; This is a spontaneous report received from contactable reporter(s) (Other HCP) from a sales representative and medical information team.  A 4-year-old male patient received bnt162b2 omi xbb.1.5 (PFIZER-BIONTECH COVID-19 VACCINE (2023-2024 FORMULA)), on 06Oct2023 at 19:30 as dose 1, single (Lot number: HH3252, Expiration Date: 14Dec2023), on 06Oct2023 at 19:30 as dose 2, single (Lot number: HH3252, Expiration Date: 14Dec2023) and on 06Oct2023 at 19:30 as dose 3, single (Lot number: HH3252, Expiration Date: 14Dec2023) at the age of 4 years, all intramuscular for covid-19 immunisation. The patient's relevant medical history was not reported. Concomitant medication(s) included: FLU [INFLUENZA VACCINE] taken for influenza immunisation, on 06Oct2023 as dose 1, single. The following information was reported: PAIN (non-serious) with onset 2023, outcome "recovered" (2023), described as "body aches/General body pain"; FATIGUE (non-serious) with onset 2023, outcome "recovered" (2023), described as "profound fatigue"; ACCIDENTAL OVERDOSE (non-serious), INCORRECT DOSE ADMINISTERED (non-serious) all with onset 06Oct2023 at 19:30, outcome "unknown" and all described as "Patient got three doses of COVID vaccine at the same time". Therapeutic measures were taken as a result of fatigue, pain.  Additional information : As of 18Oct2023 : HCP reported that two siblings (Child 1 age 2 years and Child 2 age 4 years, were inadvertently each administered a full vial of diluted 3 dose multidose vaccine vial (total dose 9 ug/each) by the medical assistant in the (clinic withheld) on 06Oct2023. Child 1 developed erythema at the injection site that developed 24 hours after injection and resolved after 48 hours. Mom gave both children NSAIDs for 5-7 days after the vaccination. Clinic staff recognized error and instituted staff training and vaccine admin error was being entered into VAERS. HCP (also the mother) asks, "what were the safety.Patient was administered 3 doses of 3 mcg vaccine at the same time in the same syringe. Took 3 doses of 3 mcg COVID vaccine administered simultaneously. Patient took treatment with Tylenol & ibuprofen.  Follow-up (18Oct2023): This is a spontaneous follow-up report from a contactable Other HCP. This Other HCP reported for a patient that: Updated information included: Reporter information (1st slider: Institution, alternate number added, Occupation updated. 3rd slider added) and additional information added.  Amendment: This follow-up report is being submitted to amend previously reported information: Flu vaccine was updated to concomitant vaccine and suspect bnt162b2 omi xbb.1.5 date and time for dose 1 and dose 2 were updated to 06Oct2023 at 19:30.  Follow-up (03Nov2023): This is a spontaneous follow-up report received from same contactable reporter other health care professional Updated information included: New reporter, Expiry date for lot number HH3252, new events(Fatigue and pain) were added and additional information updated; Sender's Comments: Linked Report(s) : US-PFIZER INC-202300332645 same reporter/product, different patient/event;