Development of New Onset, Protracted Hyperglycemia Triggered by COVID-19 Vaccination with Ultimate Resolution in an Individual without Prior Dysglycemia

Introduction : Frequently, endocrinologists are asked for advice on COVID-19 vaccination. For patients with diabetes, promoting vaccination against COVID-19 is critical; research has shown a significantly increased risk of severe infection in these patients. 
Notably, there appears to be a physiological connection between COVID-19 infection and hyperglycemia.  There have been multiple cases of patients developing hyperglycemia after contracting COVID-19.  In contrast, there are few reported cases of new onset hyperglycemia developing after the COVID-19 vaccination.

Case Description : We present the case of a 63-year-old woman with no significant past medical history. She maintained a healthy lifestyle and stable weight for several decades (BMI 24.3).
She received her first dose of the Pfizer COVID-19 vaccination in December 2020. Frequent workplace testing (weekly, between 12/4/20 and 2/12/21) documented no evidence of COVID-19 infection, and no symptoms of COVID-19 had occurred at any time before or after immunization.
Four days post-vaccination, she developed significant polyuria and polydipsia, but accepted a second dose 3 weeks later.
The patient’s symptoms persisted for months and were accompanied by weight loss. Five months later, she finally sought medical attention. Her HbA1c and serum glucose were elevated (12.9% and 295 mg/dL, respectively).
At her endocrinology appointment in May 2021, BMI was 22.4, consistent with her reported weight loss of 1 pound per week. Metformin (500 mg twice per day) and sitagliptin (100 mg per day) were prescribed and a low-carbohydrate diet was recommended.
One week later, with fasting blood glucose between 114 - 188 mg/dL, sitagliptin was discontinued. The next week, fasting blood glucose between 71 - 95 mg/dL allowed metformin discontinuation.
In September 2021, she reported continued weight loss (BMI 20.2), attributed to the low-carbohydrate diet. After 2 months off medication, both fasting and postprandial blood glucose were < 100 mg/dL. HbA1c (5.1%), C-peptide (1.1 ng/mL), and serum glucose (90 mg/dL) were all normal. She remains normoglycemic without medication.

Discussion : There have been several reports of new-onset diabetes following COVID-19 vaccination. However, to date, we identified no published case reporting complete resolution of diabetes. We hypothesize that immune changes resulting from her COVID vaccine were associated with increases in inflammatory markers causing temporary beta cell toxicity. It is unclear what the impact of a booster will be on her glycemic control, therefore we recommend she remain vigilant for symptoms of hyperglycemia after getting her third dose.