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

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Abstract
Background: While COVID-19 lockdowns have been systematically associated with increased incidence rate of type 1 diabetes, less is known about the disease rates after lockdowns. We compared the incidence of type 1 diabetes after the COVID-19 pandemic-related closure of society (i) to the time when lockdown was implemented and to (ii) the time before the pandemic in Finland. Methods and findings: 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. Previous exposure to SARS-CoV-2 was identified by combining information on COVID-19 vaccination with data on SARS-CoV-2 antibodies analyzed in blood samples. The temporal cohort included 3,467 pediatric type 1 diabetes cases, distributed across post-lockdown ( n = 586), lockdown ( n = 785), and pre-pandemic ( n = 2,096) periods. 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)]. 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). The frequency of children testing positive for infection-associated SARS-CoV-2 antibodies increased from 0.9% during the lockdown to more than 40% after the lockdown. Study limitations include a relatively short follow-up period after the lockdown and the lack of explicit modeling of the underlying long-term secular trend in type 1 diabetes incidence. Conclusions: The lockdown represents a peak in childhood type 1 diabetes incidence in Finland compared to both the pre-pandemic and post-lockdown periods. However, the reversion toward historical levels after the lockdown does not necessarily establish a return to the expected historical trajectory, nor can it fully distinguish a transient change from temporal compensation superimposed on the background secular trend. The contrasting patterns between type 1 diabetes incidence and SARS-CoV-2 antibody prevalence during and after the lockdown suggest an indirect rather than a direct role of the virus in triggering the observed changes in incidence.
Funding Information
  • Helsingin ja Uudenmaan Sairaanhoitopiiri (TYH 2021316)
  • Helsingin ja Uudenmaan Sairaanhoitopiiri (TYH2021343)
  • Horizon 2020 Framework Programme (874735)
  • Academy of Finland (350455)
  • Academy of Finland (308613)
  • Academy of Finland (351040)
  • EU HERA: DURABLE (101102733)
  • Jane ja Aatos Erkon Säätiö (20242044)
  • VTR (TYH2025391)
  • Sigrid Juséliuksen Säätiö
  • Medicinska Understödsföreningen Liv och Hälsa
  • Doctoral School of the University of Helsinki
  • Lastentautien Tutkimussäätiö
  • the Bjorkqvist Foundation
  • Helsinki University Library

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