To determine if patients with a history of Diabetes Mellitus Type I or II developed a change in blood glucose levels as reported on Continuous glucose monitoring devices (CGMS) within the first week following administration of each dose of the COVID-19 vaccine.

A retrospective review of all patient data from the Dexcom and Libre CGMS devices available at a single site, solo endocrinology practice will be obtained. This data will include fasting morning glucose, postprandial glucose, and daily glucose area under the curve for seven days following vaccination administration, as well as daily glucose area under the curve seven days prior to vaccine administration that will be used as a control. Patients >=18 y/o with a history of Diabetes Mellitus Type I or Type II will be selected. Brand of vaccine administered (Moderna or Pfizer-BioNTech) and the change in average blood glucose, peak blood glucose, and percentage of time spent in normal range as well as above average range of blood glucose level following vaccine administration will be assessed. Patients will fill out a visual analog symptom scale based on how symptomatic and uncomfortable they were following each dose of the COVID-19 vaccine. Patients will describe side effects that they experienced following each dose of the COVID-19 vaccine.

Inclusion Criteria:

• Clinical diagnosis of Diabetes Mellitus Type I or Type II
• Received the Moderna COVID-19 vaccine or Pfizer-BioNTech COVID-19 vaccine

Exclusion Criteria:

• Patients <18y/o.
• Patients that did not receive a COVID-19 vaccine.
• Patients who did not have a CGMS downloaded for a week prior and a week after vaccination.

All eligible patients in the PI's database.

No IPD will be shared.