Caller reported the 3 patients had been administered with undiluted, full vial of the Pfizer BioNTech COVID-19 vaccine each/patient got a full vial of 6 doses undiluted; Caller reported the 3 patients had been administered with undiluted, full vial of the Pfizer BioNTech COVID-19 vaccine each; fever; This is a spontaneous report from a contactable pharmacist. A 20-years-old female patient received BNT162B2 (PFIZER-BIONTECH COVID-19 VACCINE; Solution for injection; Lot Number: FA7485; Expiration Date: Oct2021; NDC: 592671003), via an unspecified route of administration on 30Jul2021 (at the age of 20-years-old) as DOSE 2, SINGLE for covid-19 immunization. The patient medical history and concomitant medications were not reported. The patient previously took the first dose of BNT162B2 on unspecified date (at the age of 20-years-old) for covid-19 immunization. The patient had been administered with undiluted, full vial of the Pfizer BioNTech COVID-19 vaccine each. On 30Jul2021, she mentioned that 6 doses of the vaccine, which was in 1 full vial, was administered to each. It was stated that  a patient that received a 3 times concentrated dose of the Pfizer COVID-19 vaccine. Stated that upon diluting the 3 doses in the vial the patient received the full vial. She had no idea why in terms she hadn't done Pfizer before and this was not her home store and she blanked her mind, and she was thinking it was a single dose vial. To be honest she did it and she walked back and then realized. Stated this is not her home store and she doesn't work at that one, it was for an emergency. She did not have height or weight to provide. Stated it was her 2nd dose of Pfizer COVID-19 vaccine given this morning, 30Jul2021. Somehow, she was walking, and she didn't know why. States she thought it was single use vial, but it was 6 doses, and it was undiluted. Clarified that the patient got a full vial of 6 doses undiluted. Clarified that she had a total of 3 people all at the same time and received a full vial of 6 doses undiluted. No further details provided on other 2 patients. She couldn't think right now to continue with the reports and a report on the website and will be doing that. Stated right now she needed more information like what the outlook and recommendations are to contact and monitor and what are the risks in terms of patient safety. She wanted to know the outlook and recommendations in terms of safety, monitoring and contacting the patients for the inadvertent administration. In response, disclaimer was provided.As of 03Aug2021, it was reported that, 0.3mL of undiluted vaccine was administered not the full vial because the dose was correct in the syringe but dilution was not. The vial still had a little liquid left over after pulling the dose, so she thinks she pulled the correct mL in the syringe of 0.3mL, but did not dilute first. The patient reported fever but has since resolved with Tylenol and ibuprofen when the doctor reported back to the pharmacy on Monday, 02Aug2021. The outcome of the event pyrexia was recovered on 02Aug2021 and all other events were unknow.  Follow-up (03Aug2021): This is follow-up spontaneous report from a contactable Pharmacist. This Pharmacist reported for a patient in response to HCP letter sent via telephonic follow-up activity which included that: New event and clinical information updated.  Follow-up activities closed, No further information expected.; Sender's Comments: Linked Report(s) : US-PFIZER INC-202100980363 same reporter/product/event, different patient;US-PFIZER INC-202100980364 same reporter/product/event, different patient