Background: Patients with type 2 diabetes mellitus (T2D) are more vulnerable to severe SARS-CoV-2 infections. However, limited evidence exists on the risk of breakthrough infections and clinical outcomes after SARS-CoV-2 infections in this susceptible population.
Objectives: To explore the risk of breakthrough infection among patients with T2D and the risk of severe clinical outcomes after the SARS-CoV-2 infection according to the COVID-19 vaccination status.
Methods: We conducted a nationwide cohort study using South Korea’s linked database of COVID-19 registry and claims data, 2018-2021. We assembled two cohorts for this study. The first cohort (or full vaccination cohort) consisted of patients with full vaccination, which is defined as 14 days after last vaccination. Patients were followed from the date of full vaccination until the date of breakthrough infection, death, or end of the study period, whichever occurred first. Using Cox proportional hazard model, hazard ratios (HRs) and 95% confidence intervals (CIs) of breakthrough infections were assessed within 1:1 propensity score (PS) matched fully vaccinated patients with vs without T2D (full vaccination cohort). The second cohort (or T2D cohort) consisted of SARS-CoV-2 infected patients with T2D. Patients were followed from the confirmed date of SARS-CoV-2 infection until severe COVID-19 outcome occurrence, death, 30th day of follow-up, or end of the study period, whichever occurred first. HRs and 95% CIs of severe COVID-19 outcomes (all-cause mortality, intensive care unit admission/mechanical ventilation use [ICU/MV use], and hospitalizations) were measured within 1:1 PS matched T2D patients with vs without full vaccination (T2D cohort).
Results: In the full vaccination cohort, 2,109,970 of patients with and without T2D were identified (age: 63.5; male: 50.9%). Patients with T2D showed a significantly increased risk of breakthrough infections compared with those without T2D (HR 1.10, 95% CI, 1.06-1.14). Specifically, the effect estimate was higher in T2D patients receiving insulin treatment (1.23, 1.10-1.39). In the T2D cohort, 10,850 of patients with and without full vaccination were identified (age: 63.5; male: 50.9%). The risk for severe COVID-19 outcomes was lower in fully vaccinated patients compared with unvaccinated patients (all-cause mortality: 0.54, 0.43-0.67; ICU/MV: 0.31, 0.23-0.41; hospitalization: 0.73, 0.68-0.78).
Conclusions: While patients with T2D remain a vulnerable population to SARS-CoV-2 infection even after the full vaccination, full vaccination was associated with a lower risk of clinical outcomes after SARS-CoV-2 infection. These findings herein support the guidelines recommending patients with T2D as a priority vaccination group.
