From the Journals

COVID booster may transiently raise glucose levels in T1D




The COVID-19 booster vaccine typically causes transient, clinically insignificant elevations in glucose levels in people with type 1 diabetes, but some individuals may develop more pronounced hyperglycemia.


  • In a single-center prospective cohort study of 21 adults with type 1 diabetes, patients were given a blinded Dexcom G6 Pro continuous glucose monitor (CGM) at the first research clinic visit.
  • After 3-4 days, participants received a COVID-19 booster vaccine.
  • They returned to the clinic 10 days after the initial visit (5-6 days after booster vaccination) to have the CGM removed and glycemia assessed.


  • Compared with baseline, the mean daily glucose level was significantly increased at day 2 (162.9 mg/dL vs. 172.8 mg/dL; P = .04) and day 3 (173.1 mg/dL; P = .02) post vaccination.
  • Glucose excursions at day 0 (173.2 mg/dL; P = .058) and day 1 (173.1 mg/dL; P = .078) didn’t quite reach statistical significance.
  • One participant experienced increases in glucose of 36%, 69%, 35%, 26%, 22%, and 19% on days 0-5, respectively, compared with baseline.
  • Glucose excursions of at least 25% above baseline occurred in four participants on day 0 and day 1 and in three participants on days 2 and 5.
  • Insulin resistance, as measured by Total Daily Insulin Resistance (a metric that integrates daily mean glucose concentration with total daily insulin dose), was also significantly increased from baseline to day 2 post vaccination (7,171 mg/dL vs. 8,070 mg/dL units; P = .03).
  • No other measures of glycemia differed significantly, compared with baseline.
  • Outcomes didn’t differ significantly by sex, age, or vaccine manufacturer.


  • “To our knowledge this is the first study investigating the effect of the COVID-19 booster vaccine on glycemia specifically in people with type 1 diabetes,” say the authors.
  • “Clinicians, pharmacists, and other health care providers may need to counsel people with T1D to be more vigilant with glucose testing and insulin dosing for the first 5 days after vaccination. Most importantly, insulin, required to control glycemia, may need to be transiently increased.”
  • “Further studies are warranted to investigate whether other vaccines have similar glycemic effects, and which individuals are at highest risk for profound glucose perturbations post vaccination.”


The study was conducted by Mihail Zilbermint, MD, of the division of hospital medicine, Johns Hopkins Medicine, Bethesda, Md., and colleagues. It was published in Diabetes Research and Clinical Practice.


  • The sample size was small.
  • There were no measurements of inflammatory markers, dietary intake, physical activity, or survey patient symptomatology to adjust for variables that may have influenced glycemic control.
  • In the study cohort, glycemia was moderately well controlled at baseline.


The study was supported by an investigator-initiated study grant from DexCom Inc. Dr. Zilbermint has consulted for EMD Serono.

A version of this article first appeared on

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