Adverse reactions, including the onset of diabetes, after coronavirus disease 2019 (COVID‐19) vaccination have been reported. Herein, we report a case of a man who developed anti‐glutamic acid decarboxylase (GAD) antibody‐positive fulminant type 1 diabetes 15 weeks after COVID‐19 vaccination, atypical of the previously reported anti‐GAD antibody‐negative cases.

IntroductionWe report a case series of severe ketoacidosis after COVID-19 vaccination in a type 1 diabetes patients treated with insulin and an SGLT-2 inhibitor.Case ReportWe present two cases of type 1 diabetes mellitus. One patient was treated with insulin therapy and an SGLT-2 inhibitor, and the other patient was treated with insulin therapy alone. Both patients became ill after coronavirus disease-2019 vaccination, making it difficult to continue their diet or insulin injections. On admission, they developed severe diabetic ketoacidosis. This is the first report of ketoacidosis after coronavirus disease-2019 vaccination.ConclusionThe vaccine should be carefully administered to type 1 diabetes patients receiving intensive insulin therapy and a sodium-glucose transporter due to the high risk ketoacidosis. It is important to instruct patients to drink sufficient fluids and to continue insulin injections when they become sick.