The change in glycaemic control immediately after COVID‐19 vaccination in people with type 1 diabetes

Aims Evidence suggests that some people with type 1 diabetes mellitus (T1DM) experience temporary instability of blood glucose (BG) levels after COVID‐19 vaccination. We aimed to assess this objectively. Methods We examined the interstitial glucose profile of 97 consecutive adults (age ≥ 18 years) with T1DM using the FreeStyle Libre® flash glucose monitor in the periods immediately before and after their first COVID‐19 vaccination. The primary outcome measure was percentage (%) interstitial glucose readings within the target range 3.9–10 mmol/L for 7 days prior to the vaccination and the 7 days after the vaccination. Data are mean ± standard error. Results There was a significant decrease in the % interstitial glucose on target (3.9–10.0) for the 7 days following vaccination (mean 52.2% ± 2.0%) versus pre‐COVID‐19 vaccination (mean 55.0% ± 2.0%) (p = 0.030). 58% of individuals with T1DM showed a reduction in the 'time in target range' in the week after vaccination. 30% showed a decrease of time within the target range of over 10%, and 10% showed a decrease in time within target range of over 20%. The change in interstitial glucose proportion on target in the week following vaccination was most pronounced for people taking metformin/dapagliflozin + basal bolus insulin (change −7.6%) and for people with HbA1c below the median (change −5.7%). Conclusion In T1DM, we have shown that initial COVID‐19 vaccination can cause temporary perturbation of interstitial glucose, with this effect more pronounced in people talking oral hypoglycaemic medication plus insulin, and when HbA1c is lower.