fatigue; She accidentally mixed the vial with 1.3 ml of diluent instead of 2.2 ml and realized this after she had administered 5 doses; She accidentally mixed the vial with 1.3 ml of diluent instead of 2.2 ml; This is a spontaneous report received from a contactable reporter(s) (Nurse) from medical information team.  A 24-month-old patient received BNT162b2 (BNT162B2), on 07Oct2022 at 08:54 as dose 1 (maroon cap), single (Lot number: FT9142, Expiration Date: 31Dec2022) at the age of 24 months intramuscular, in left thigh for covid-19 immunisation. The patient's relevant medical history included: "GERD", start date: 13Jul2021 (ongoing), notes: Pertinent details: N/A. The patient's concomitant medications were not reported. Vaccination history included: pentacel (Manufacture: Sanofi, Batch/lot: UJ641AAA, Route: IM, Anatomical site of injection: Left thigh, No. of previous doses: 3), administration date: 14Sep2022; prevnar 13 (Manufacture: Pfizer, Batch/lot: FF7356, Route: IM, Anatomical site of injection: Right thigh, No. of previous doses: 3), administration date: 14Sep2022; fluzone (Manufacture: Sanofi, Batch/lot: UT7680MA, Route: IM, Anatomical site of injection: Left thigh, No. of previous doses: 2), administration date: 14Sep2022. The following information was reported: PRODUCT PREPARATION ISSUE (non-serious) with onset 07Oct2022 at 08:54, outcome "unknown", described as "She accidentally mixed the vial with 1.3 ml of diluent instead of 2.2 ml"; OVERDOSE (non-serious) with onset 07Oct2022 at 08:54, outcome "unknown", described as "She accidentally mixed the vial with 1.3 ml of diluent instead of 2.2 ml and realized this after she had administered 5 doses"; FATIGUE (non-serious) with onset 08Oct2022, outcome "recovered" (09Oct2022). Therapeutic measures were not taken as a result of fatigue.  Additional information: The nurse reported a vaccination error involving the Pfizer COVID-19 vaccine maroon cap for 6 months to under 5 years. She was running a COVID clinic for little ones and she had consulted the COVID vaccine prep and administration summaries from the CDC website and she had gotten confused about the diluent amount and accidentally mixed the vial with 1.3 ml of diluent instead of 2.2 ml and realized that after she had administered 5 doses and could not draw anymore, up to 5 kids (1 was almost 2, 1 patient was 2, 1 patient was 3, 1 patient was 15 months and 1 patient was 6 months) were administered with the vaccine; she stated that it was the last vaccine for 2 of the patients. The reporter considered that the Pfizer product had a causal effect to the adverse event. Relevant tests were not done.  Follow-up (10Oct2022): This is a spontaneous follow-up report received in response to the mail trail sent regarding the confirmation of query. The response included:  Updated information: Reporter information updated.  Follow-up (14Oct2022): Follow-up attempts are completed. No further information is expected.  Follow-up (09Dec2022): This is a spontaneous follow-up report received from the same contactable Nurse. This Nurse reported for the patient in response to HCP letter sent via follow-up letter which included that: Updated information included: Reporter's details, historical vaccine details, suspect product details and additional information were updated.; Sender's Comments: Linked Report(s) : US-PFIZER INC-202201213448 same reporter, drug, and event; different patient;US-PFIZER INC-202201213449 same reporter, drug, and event; different patient;US-PFIZER INC-202201213450 same reporter, drug, and event; different patient;US-PFIZER INC-202201213451 same reporter, drug, and event; different patient;US-PFIZER INC-PV202200122002 Same patient/drug, different dose/event;