Blood ketone body increased; Her normal blood glucose levels average between 165-175. She said her blood glucose levels had spiked to highs in the 300s, and lows down to a "LOW" reading on the glucometer.; This is a spontaneous report received from contactable reporter(s) (Consumer or other non HCP).  A 16 year-old female patient received bnt162b2 (BNT162B2), administered in arm right, administration date 01May2021 (Batch/Lot number: unknown) at the age of 16 years as dose 1, single for covid-19 immunisation. Relevant medical history included: "Type 1 diabetes mellitus" (ongoing), notes: Verbatim: Type 1 diabetes mellitus, She has had Type 1 Diabetes for 3 years and 4 months. The patient took concomitant medications. The following information was reported: BLOOD GLUCOSE FLUCTUATION (non-serious) with onset 02May2021, outcome "unknown", described as "Her normal blood glucose levels average between 165-175. She said her blood glucose levels had spiked to highs in the 300s, and lows down to a "LOW" reading on the glucometer."; BLOOD KETONE BODY INCREASED (non-serious) with onset 04May2021, outcome "unknown", described as "Blood ketone body increased". Relevant laboratory tests and procedures are available in the appropriate section. Therapeutic measures were taken as a result of blood glucose fluctuation.  Additional information: The reporter was aunt of the patient. The vaccine was Administered between 1:00 PM-1:30 PM. The patient got her (first) COVID-19 Vaccine on Saturday (01May2021). The patient was a Type 1 Diabetic, and her (blood glucose) numbers were up and down (since she received her first COVID-19 Vaccine on 01May2021). The patient had been following Type 1 diabetic treatment protocols that she had done in the past (for her blood glucose levels), and the Type 1 diabetic treatment protocols were still not correcting her blood glucose levels now. The only thing different that had happened from last week was that had the COVID-19 Vaccine. She said she looked online for specific Type 1 diabetic interactions with the COVID-19 Vaccine and was only able to find information for Type 2 diabetics and the COVID-19 Vaccine. Patient's mother reported her daughter's blood glucose levels were good on Saturday (01May2021). She said on Sunday (02May2021) her daughter's blood glucose levels started to fluctuate. She said since Sunday (01May2021), her daughter's blood glucose levels had spiked to highs in the 300s, and lows down to a "LOW" reading on the glucometer. Patient's mother stated a "LOW" reading on the glucometer was below 39. She said her daughter's blood glucose level continued to be either up, and then down, and then back up, and then back down. She said her daughter's blood glucose level had not leveled off. The treatment for Blood Glucose Fluctuation reported as of 04May2021, her daughter was put on a "sick day" protocol. She stated her daughter was given insulin (clarified as Novolog) in addition to her daughter's insulin pump (clarified as an Omnipod). She said her daughter's Omnipod insulin pump used a "DIY" looping system, and the Omnipod would auto-click in and increase insulin (administered) as high as was good to go. She said the Omnipod was an insulin delivery system, and didn't manage her daughter's insulin levels, but used suggested algorithms. She clarified she would give her daughter an additional "subq" (subcutaneous) Novolog insulin injection based on her daughter's high blood glucose levels. She stated she did not have the NDC, Lot, and Expiration Dates for the insulin. Reported when her daughter's blood glucose level was low, her daughter used glucose tablets and Gatorade. Reported she monitored her daughter's blood ketone levels, and today (04May2021), her daughter's blood ketone level was 0.3. She said her daughter's normal blood ketone level comes in at 0.1. She said she only checks her daughter's blood ketone levels if her daughter has a period of blood glucose level highs for more than 6 hours. No further details provided. Reported her daughter last had lab testing on 07Jan2021. No further details provided. Reported her daughter's menstrual cycle started on Saturday (01May2021). She stated her daughter's menstrual cycle could be a factor in her daughter's fluctuating blood glucose levels. No further details provided. Vaccination Facility Type was Other. The patient did not have history of all previous immunization with the Pfizer vaccine. The patient did not have prior vaccination (within 4 weeks).  No follow-up attempts are possible; information about lot/batch number cannot be obtained. No further information is expected.