Study shows COVID-19 vaccination reduces, but does not entirely ameliorate, excess diabetes incidence after COVID-19

By Dr. Sanchari Sinha Dutta, Ph.D.Reviewed by Benedette Cuffari, M.Sc.Aug 15 2023

In a recent study posted to the medRxiv preprint server, researchers investigate the effect of coronavirus disease 2019 (COVID-19) and its vaccination on the incidence and persistence of type 2 diabetes.

Study: Diabetes following SARS-CoV-2 infection: Incidence, persistence, and implications of COVID-19 vaccination. A cohort study of fifteen million people. Image Credit: Proxima Studio / Shutterstock.com

*Important notice: medRxiv publishes preliminary scientific reports that are not peer-reviewed and, therefore, should not be regarded as conclusive, guide clinical practice/health-related behavior, or treated as established information.

Background

To date, the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the causative pathogen of COVID-19, has caused over 765 million infections worldwide. Among various COVID-19 related risk factors, the presence of diabetes significantly increases the morbidity and mortality of SARS-CoV-2 infection.

Studies conducted during the pandemic have estimated a 30-50% surplus incidence of type 2 diabetes following SARS-CoV-2 infection; however, this effect has not been observed for type 1 diabetes. It remains unclear whether this rise in diabetes cases is a short-term or durable consequence of SARS-CoV-2 infection.

In the current observational cohort study, scientists evaluate the association between COVID-19 and incident diabetes, as well as the impact of diabetes type, time since COVID-19 diagnosis, and vaccination status on this association.

Study design

The study population included all adults registered with a primary care general practice in England. COVID-19 vaccination was introduced in England on December 8, 2020, with all adults eligible to receive their first dose by June 18, 2021, and second dose by August 2021.   

In the pre-vaccination cohort between January 2020-December 2021, electronic health records and COVID-19 related data of 15,211,471 individuals were analyzed to estimate diabetes incidence. In the vaccinated and unvaccinated cohorts who were studied between June and December 2021, the health data of 11,822,640 and 2,851,183 individuals, respectively, were analyzed for the same parameter.

The incidence of different types of diabetes was determined in the study, including type 1 and type 2 diabetes, gestational diabetes, and other non-specific diabetes. In the pre-vaccination cohort, the incidence of persistent type 2 diabetes, which was defined as diabetes with continued treatment or elevated hemoglobin A1c (HbA1c) levels four months after diagnosis, was also analyzed.

The current study also estimated the risk of developing diabetes by comparing pre- and post-COVID-19 diabetes incidence, with the results stratified by COVID-19 severity and type of diabetes.

Important observation

In the pre-vaccination, vaccinated, and unvaccinated cohorts, 827,074, 750,370, and 147,044 individuals were diagnosed with COVID-19 during the study period, respectively. More specifically, 133,323, 32,466, and 2,140 cases of incident type 2 diabetes were reported, respectively. Corresponding numbers of incident type 1 diabetes cases were 14,917, 2,410, and 45, respectively.

A significantly higher incidence of both type 1 and type 2 diabetes was observed after COVID-19 related hospitalization in all cohorts as compared to non-hospitalized and without COVID-19 cases.

The prevalence of persistent type 2 diabetes cases was 73%, 69%, and 74% among COVID-19 diagnosed, hospitalized, and non-hospitalized individuals, respectively. In the pre-vaccination cohort, persistent type 2 diabetes was observed among 74% of individuals diagnosed with incident type 2 diabetes.

Impact of COVID-19 and its vaccination on type 2 diabetes incidence

An increased incidence of type 2 diabetes was observed in each study cohort during the first four weeks after COVID-19 diagnosis, with the unvaccinated cohort associated with a significantly higher incidence than the vaccinated cohort.

In the pre-vaccination cohort, a three-times higher risk of incident type 2 diabetes was observed among COVID-19 patients during the first four weeks of diagnosis as compared to those without COVID-19. In this cohort, the proportion of incident diabetes remained elevated 53-102 weeks after the initial COVID-19 diagnosis. 

In each study cohort, the proportion of incident diabetes was significantly higher among hospitalized COVID-19 patients as compared to non-hospitalized patients. This proportion remained elevated, even four weeks after the initial COVID-19 diagnosis in each cohort. Most cases of incident diabetes following COVID-19 were persistent.

In each cohort, the absolute additional risk of diabetes was higher among individuals over 60 years of age as compared to younger individuals. However, no impact of other confounding factors, including sex, ethnicity, and presence of pre-diabetes and obesity on incident diabetes, was observed across the study cohorts.

Regarding type 1 diabetes, a higher incidence after COVID-19 was observed in the pre-vaccination and unvaccinated cohorts as compared to the vaccinated cohort. In the pre-vaccination cohort, a significantly higher incidence of type 1 diabetes was observed among hospitalized COVID-19 patients as compared to non-hospitalized patients. No significant impact of COVID-19 was observed on the incidence of gestational diabetes.

Study significance

The current study reports a persistently higher risk of incident type 2 diabetes among hospitalized COVID-19 patients as compared to non-hospitalized patients. Notably, a significant reduction in incident diabetes risk has been observed post-vaccination.

*Important notice: medRxiv publishes preliminary scientific reports that are not peer-reviewed and, therefore, should not be regarded as conclusive, guide clinical practice/health-related behavior, or treated as established information.