Instead of mixing 1.3mL of diluent, only 0.1mL was mixed to the vaccine, resulting to a higher than authorized dose being given to a patient; Instead of mixing 1.3mL of diluent, only 0.1mL was mixed to the vaccine, resulting to a higher than authorized dose being given to a patient; Anatomical Location: Left Thigh; Slightly exaggerated immune response; This is a spontaneous report received from contactable reporter(s) (Nurse and Physician) from medical information team.  An 8-year-old male patient received BNT162b2 (BNT162B2), on 26May2022 at 15:31 as dose 3 (booster), single (Lot number: FL8095, Expiration Date: 30Aug2022) at the age of 8 years intramuscular, in left thigh for covid-19 immunisation. The patient had no relevant medical history. There were no concomitant medications. Vaccination history included: BNT162b2 (dose 1, single, lot: FK5127, NDC:59267-1055-4, expiration: 30Jan2022, Route of adminstration: left thigh), administration date: 06Dec2021, when the patient was 7-year-old, for Covid-19 Immunization; BNT162b2 (dose 2, single, lot: FK5618, NDC: 59267-1055-4, Expiration: 21Feb2022, Route of adminstration: right vastus lateralis), administration date: 27Dec2021, when the patient was 7-year-old, for Covid-19 Immunization. The following information was reported: INCORRECT ROUTE OF PRODUCT ADMINISTRATION (non-serious) with onset 26May2022 at 15:31, outcome "unknown", described as "Anatomical Location: Left Thigh"; OVERDOSE (non-serious), PRODUCT PREPARATION ISSUE (non-serious) all with onset 26May2022 at 15:31, outcome "unknown" and all described as "Instead of mixing 1.3mL of diluent, only 0.1mL was mixed to the vaccine, resulting to a higher than authorized dose being given to a patient"; IMMUNE SYSTEM DISORDER (non-serious) with onset 2022, outcome "unknown", described as "Slightly exaggerated immune response". Therapeutic measures were not taken as a result of immune system disorder.  Another reporter (Health Care professional) considered "instead of mixing 1.3ml of diluent, only 0.1ml was mixed to the vaccine, resulting to a higher than authorized dose being given to a patient", "anatomical location: left thigh" and "slightly exaggerated immune response" as unrelated to BNT162b2.  Additional information: Caller said their patient was administered Pfizer covid vaccine pediatric formulation that has only been mixed with too little diluent; instead of mixing 1.3mL of diluent, only 0.1mL was mixed to the vaccine, resulting to a higher than authorized dose being given to a patient as a booster shot yesterday. Caller wants to know guidelines for the administration error. The caller is an HCP who states yesterday, 26May2022 at 17:26 a patient was administered the Pediatric Pfizer Covid 19 Vaccine mixed with more than the required diluent. Received vaccine mixed with 0.1ml of diluent instead of 1.3ml diluent: Caller clarifies caller doesn't have the time administered but the date the patient was administered the Pediatric Pfizer Covid 19 Vaccine mixed with more than the required diluent was yesterday, 26May2022. The 8-year-old patient came into the clinic. Nurses noticed this morning, 27May2022 that the diluent was not diluted correctly for the patients Pediatric Pfizer Covid 19 Vaccine administered yesterday, 26May2022. The nurse who administered the vaccine was asked how much diluent was used, 0.1ml of diluent was used instead of 1.3ml diluent for the Pediatric Pfizer Covid 19 Vaccine administered to the patient. Caller clarifying 0.1ml diluent was used instead of 1.3ml diluent, not more than the required diluent as stated by CEP transfer agent. Diluted with sterile water, not diluted enough. Preparation error. Did not have dilution instruction or appropriate diluent with concentrated vaccine vial. Slightly exaggerated immune response, otherwise none.  Follow-up attempts are completed. No further information is expected.  Follow-up (29Jun2022):  This is a spontaneous follow-up report received from a contactable physician. This physician reported in response to HCP letter sent via follow up letter. Updated information included: updated reporter information (slide#03), causality for 3rd reporter HCP, vaccination time, vaccination facility details. added events Inappropriate route of vaccination and Slightly exaggerated immune response. Route of administration captured as intramuscular. At risk removed as classification.