Trends in the incidence of childhood type 1 diabetes after the COVID-19 lockdown in Finland: An observational study

Background Coronavirus disease 2019 (COVID-19) and subsequent social distancing has been associated with increased incidence of type 1 diabetes in a series of studies. However, little is known about the disease rates after the end of lockdowns.Methods The incidence of type 1 diabetes after the lockdown (09/2021-12/2022) was compared to the incidence during the lockdown (03/2020-08/2021) and before the lockdown (three 18-month terms 2014-2019) in Finnish children under the age of 15 years. In addition, we compared the clinical characteristics, signs of islet autoimmunity and frequency of risk-associated HLA genotypes during these time periods. Preceding SARS-CoV-2 infections were identified by SARS-CoV-2 antibodies analyzed in blood samples taken at the time of the diagnosis of type 1 diabetes.Results The incidence of type 1 diabetes after the lockdown was significantly lower than the incidence during the lockdown [incidence rate ratio (IRR=0‧85; 95% Cl=0‧77-0‧95, P=0‧004). A difference was observed for males (IRR=0‧82; 95% Cl=0‧72-0‧95, P=0‧007) but not for females (IRR=0‧90; 95%Cl=0‧76-1‧05, P=0‧185). The rate of type 1 diabetes after the lockdown did not significantly differ from the time before lockdown (IRR=1‧00; 95% Cl=0‧91-1‧09, P=0‧932). Children diagnosed after the end of the lockdown were older, had more often severe ketoacidosis and had had symptoms for a shorter period preceding the diagnosis compared to children diagnosed before the COVID-19 pandemic. These children tested also positive for GAD autoantibodies less frequently than those diagnosed with type 1 diabetes during the lockdown. The frequency of children testing positive for infection-associated SARS-CoV-2 antibodies increased from 0.9% during the lockdown to 39.9% after the lockdown.Interpretation The contrasting patterns of the incidence of type 1 diabetes and the prevalence of COVID-19 infections during and after the lockdown contradict a direct role of the SARS-CoV-2 virus in triggering the changes observed in the incidence of type 1 diabetes during the COVID-19 pandemic in Finland.