New-onset Fulminant Type 1 Diabetes Following COVID-19 Vaccination.

A 31-year-old Japanese man was admitted with a slight fever and epigastric pain. He had received his third Moderna Coronavirus disease 2019 (COVID-19) vaccine dose (Spikevax, mRNA-1273) 16 days before his visit. His serum amylase level was elevated, and computed tomography found pancreatic enlargement. Acute pancreatitis was diagnosed, and the patient was treated with fasting and intravenous fluids. However, on day 3 of hospitalization, his blood glucose level had increased to 320 mg/dL. His serum and urinary C-peptide were remarkably low (≤0.03 ng/mL and ≤0.6 μg/day, respectively). Finally, fulminant type 1 diabetes mellitus caused by the COVID-19 mRNA vaccine was diagnosed.