The connection between SARS-CoV-2 infection and the onset of type 1 diabetes has been a topic of investigation by researchers since the start of the COVID-19 pandemic. Some studies reported an increase in new cases of type 1 diabetes during the pandemic, but it was unclear whether this increase was directly related to coronavirus infection.
Now a new study conducted by Danish researchers presents a different picture. In a national data–based case–control study, the investigators reviewed records of 2,115 individuals diagnosed with type 1 diabetes before age 30 between 2020 and 2023, and matched each with five individuals without diabetes, a total of 10,575 people, by age and sex.
16 percent reduction over a four-year period
Results showed that individuals with a history of SARS-CoV-2 infection had, over the entire four-year follow-up period, a 16 percent lower risk of developing type 1 diabetes. However, when researchers examined different time windows after infection separately, this association was observed mainly in the 31 to 180 days after infection.
In that window, the risk of developing type 1 diabetes was about 42 percent lower. The association was not seen in other post-infection time windows; a finding that indicates the new result should not be simply interpreted as a permanent reduction in the risk of type 1 diabetes.
Another notable finding was that the observed association appeared only in unvaccinated individuals. Also, the relationship was statistically significant in women but did not reach statistical significance in men. Researchers found no significant differences among different age groups under 30.
Why is this finding unexpected?
Type 1 diabetes is an autoimmune disease in which the immune system attacks the insulin-producing beta cells in the pancreas. Since the early days of the pandemic, scientists have been examining whether SARS-CoV-2 could play a role in causing this disease by altering immune function or through other mechanisms.
But previous studies have not produced consistent results. For example, a nationwide Danish study published in 2023 found no significant increase in the risk of type 1 diabetes after SARS-CoV-2 infection in children.
On the other hand, a study published in Sweden in 2026 reported a short-term increase in type 1 diabetes diagnoses after infection; although its authors attributed the increase more to diagnosis or unmasking of disease and did not find evidence for a sustained causal effect.
Does COVID really reduce diabetes risk?
The current answer is unclear. The new study identified a statistical association but cannot prove that coronavirus infection directly caused a reduced risk of type 1 diabetes.
One main reason for this limitation is the observational nature of the study. In such studies researchers examine data on events that occurred in the real world, but they do not randomly expose people to the virus. Therefore other factors not measured in the analysis may explain part of the observed difference.
At the same time, the researchers listed important strengths of their study, including the use of Denmark's high-quality national registries, very broad coverage of PCR testing, and complete information about individuals' vaccination status.
The study is being presented at the annual meeting of the European Association for the Study of Diabetes (EASD) in Milan, and its findings raise a new question about the relationship among viral infections, the immune system, and type 1 diabetes rather than indicating a "benefit" of acquiring COVID-19.
Consequently, the new finding should be considered alongside the existing body of evidence and in no way means that contracting COVID-19 could be a way to prevent type 1 diabetes. The researchers themselves emphasize the need for further studies to clarify a possible mechanism for this association and to examine results in other populations.