New study summary:
Study: Nationwide cohort study in Norway, to be presented at the EASD Annual Meeting in Milan and published in Diabetologia. Lead author is PhD student Maria Östman, University of Oslo.
Background: Rotavirus causes gastroenteritis in young children. Norway introduced the oral live-attenuated monovalent Rotarix® vaccine into its national childhood immunization programme in September 2014, with rapid, high uptake — 92.8%. Previous studies on rotavirus vaccine and type 1 diabetes risk have had conflicting results.[T1D]
Methods: Researchers followed all children born in Norway 2007-2019 — 740,744 children — from 0.5 to 5 years of age for T1D diagnosis, with follow-up through Dec 31, 2024. They compared T1D incidence in children born before vs. after the September 2014 rotavirus vaccine introduction.
Main findings:
- 846 children were diagnosed with T1D before age 5.
- Using interrupted time series analysis, the observed incidence after vaccine introduction was 11% higher than the predicted trend based on pre-vaccination data.
- When comparing fully vaccinated children [2 doses of Rotarix] to non-vaccinated children, the adjusted hazard ratio was 1.17, which was not statistically significant.
The authors stated: “This study found no evidence for a reduced risk of type 1 diabetes after introduction of rotavirus vaccination in infancy but found instead that the incidence… increased after rotavirus vaccination was introduced.”
Secondary / negative control analyses — why authors think vaccine is probably not the cause:
To test whether the increase was specific to rotavirus vaccine, they looked at two other unrelated changes to the Norwegian immunisation programme as negative controls:
- Introduction of hepatitis B vaccine in 2016
- Switch from 7-valent to 13-valent pneumococcal vaccine in 2011
Both of those changes were also followed by a similar magnitude increase in T1D incidence, despite no biological reason to expect them to affect T1D risk.
The authors conclude this pattern suggests the 11% increase seen after September 2014 is likely due to other, yet unknown environmental factors and not the rotavirus vaccine itself, and not explained by the combination of vaccine programme changes.
They also considered other potential explanations, including the COVID-19 pandemic — Norway saw a temporary T1D increase in 2022 — and a 2018 change in prenatal ferritin screening guidelines related to iron supplementation, but did not think these explained the findings.
Authors’ interpretation: “We do not believe that rotavirus vaccination increases the risk of type 1 diabetes. We believe there is a need for additional studies on rotavirus vaccination and type 1 diabetes in different settings with different vaccines before concluding anything.” They emphasized the need for more research on environmental factors influencing T1D, which has been generally increasing over past decades.