COVID-19 Infection Linked to Lower Risk of T1D in Those Younger Than 30

New research to be presented at the Annual Meeting of the European Association for the Study of Diabetes (EASD) in Milan, Italy, has found that individuals who contracted COVID-19 had a lower—rather than higher—subsequent risk of developing type 1 diabetes (T1D), with the protective association appearing only among those who had not received a SARS-CoV-2 vaccine.¹

The findings, which are from a Danish nationwide registry study, counter concerns raised earlier in the pandemic that SARS-CoV-2 infection might trigger new-onset autoimmune diabetes in young people.²

Study Design and Population

The nested case-control study used Denmark's high-quality national health registries to identify 2115 individuals diagnosed with T1D before age 30 years between January 1, 2020, and December 31, 2023. Each case was matched by age and sex to 5 diabetes-free controls, for a comparison group of 10,575 individuals. Investigators excluded anyone with a prior diagnosis of diabetes, autoimmune disease, cancer, or use of immunomodulatory therapy.¹

Exposure was defined as a first positive SARS-CoV-2 polymerase chain reaction (PCR) test recorded between January 2020 and December 2021, a window spanning the index, alpha, and delta variants but preceding omicron's dominance. Because Denmark maintained extensive PCR testing infrastructure and complete vaccination records throughout the pandemic, the authors noted that the registries offered an unusually precise way to separate the effects of infection from those of vaccination.³

Key Findings

Across the full 4-year observation period, SARS-CoV-2 infection was associated with a statistically significant 16% reduction in the risk of subsequent T1D, a finding that held when all viral variants were analyzed together, although there were no single variants that reached statistical significance on their own. The protective signal was strongest early after infection: Individuals had an approximately 42% lower risk of developing T1D in the 31- to 180-day window following a positive test, with no significant association observed in other time periods.¹

When investigators stratified results by vaccination status, the reduced risk was confined to unvaccinated individuals, who had a 24% lower risk of T1D following infection compared with unvaccinated, uninfected individuals. Estimates among vaccinated individuals were too imprecise to draw firm conclusions, and there was no statistical evidence that vaccination status modified the association. The protective association was also more pronounced by sex: Females who had been infected had a statistically significant 26% reduced risk of T1D, whereas the reduction in males was not considered significant. There were no meaningful differences between younger (aged 0-10 years) and older (aged 11-30 years) participants that emerged.^1,4,5

Possible Mechanisms

The study authors proposed that certain viral infections may activate regulatory immune mechanisms that temporarily dampen the autoimmune processes responsible for T1D before the immune system returns to its baseline state. They suggested that vaccination, by inducing adaptive immunity through a different pathway, may potentially interfere with this same viral activation of regulatory mechanisms—one possible explanation for why the protective association disappeared in vaccinated individuals.^1,5

The authors were careful to frame the results as hypothesis-generating rather than definitive. They said, “The study is observational in nature, which means we cannot say for sure that the reduced risk of T1D was caused by SARS-CoV-2 infection.” They added that they hope the findings will prompt similar analyses using high-quality registry data from other countries.^1,3

Context Within a Mixed Evidence Base

The new findings add to what the authors describe as inconsistent literature on this question. A 2023 Danish registry study from an overlapping research group found no significant association between SARS-CoV-2 infection and subsequent T1D risk, but that analysis was limited by a shorter observation window and a small number of events. Other international cohorts have similarly reported conflicting signals, with a minority of studies pointing toward increased T1D risk after infection. The authors of the current study emphasized that Denmark’s combination of near-universal PCR testing and detailed vaccination records helped address some of the power and misclassification limitations that hindered earlier work.^1,3

Clinical Takeaways for Pharmacists

Although the study does not change screening or treatment recommendations for T1D, pharmacists who are counseling patients and caregivers on post–COVID-19 concerns can use these findings to contextualize the current evidence: To date, high-quality registry data have not shown that SARS-CoV-2 infection increases T1D risk in individuals younger than 30 years of age, and this analysis suggests infection may even be associated with a modest, transient reduction in risk among unvaccinated individuals.¹

Given the observational design, pharmacists should continue to emphasize routine, evidence-based recommendations, including vaccination against SARS-CoV-2 and standard vigilance for T1D symptoms, while awaiting corroborating data from other national registries.⁴

REFERENCES

1. Study shows that having COVID-19 is associated with lower, not higher, subsequent development of type 1 diabetes among those aged under 30 years. News release. EurekAlert! September 8, 2026. Accessed September 10, 2026. https://www.eurekalert.org/news-releases/1142932

2. Zareini B, Sørensen KK, Eiken PA, et al. Association of COVID-19 and development of type 1 diabetes: a Danish nationwide register study. Diabetes Care. 2023;46(8):1477-1484. doi.org:10.2337/dc23-0428

3. Analysis links COVID-19 infection in unvaccinated people to lower subsequent type 1 diabetes risk. News release. Medical Xpress. September 9, 2026. Accessed September 10, 2026. https://medicalxpress.com/news/2026-09-analysis-links-covid-infection-unvaccinated.html

4. COVID-19 linked to lower subsequent risk of type 1 diabetes. News release. News-Medical. September 8, 2026. Accessed September 10, 2026. https://www.news-medical.net/news/20260908/COVID-19-linked-to-lower-subsequent-risk-of-type-1-diabetes.aspx

5. Nolsøe CV, Nolsöe RML. EASD 26: SARS-CoV-2 associated with reduced risk of type 1 diabetes in under-30s. MedicalResearch.com. September 9, 2026. Accessed September 10, 2026. https://medicalresearch.com/easd-26-sars-cov-2-associated-with-reduced-risk-of-type-1-diabetes-in-under-30s/