Purpose: Spontaneous reporting of a possible link between myelin oligodendrocyte glycoprotein (MOG) antibody-associated disease (MOGAD) and mRNA SARS-CoV-2 vaccination warrants further examination. Hence, the objective of this study was to investigate the association between MOG-IgG positivity as a proxy for MOGAD and mRNA SARS-CoV-2 vaccination in the Danish population.
Methods: We applied the self-controlled case series study using Danish nationwide health registers. The study population consisted of all Danish residents who were offered an mRNA COVID-19 vaccination and had a first positive MOG-IgG test result between November 1, 2020 to December 31, 2023.
Results: Among 5.9 million individuals eligible for SARS-CoV-2 vaccination, we identified 111 incident events of MOG-IgG positivity in the study period of which 28 (25%) occurred in children. We found no association between mRNA SARS-CoV-2 vaccination and MOG-IgG positivity in adults, but an increased risk-although based on small numbers-was found in children below 18 years of age (incidence rate ratio = 8.07, 95% confidence intervals: 3.07-21.21). If the observed association reflects a causal effect, the estimated number of excess MOG-IgG positive events attributable to mRNA COVID-19 vaccination in Denmark was 4.38 per 1 000 000 exposed children.
Conclusions: These results suggest an increased risk of MOG-IgG positivity after mRNA SARS-CoV-2 vaccination in children, but not in adults. The number of additional MOGAD events attributable to mRNA SARS-CoV-2 vaccination in children is very low and further studies are needed to confirm these findings.
Keywords: COVID‐19 vaccination; MOGAD; MOG‐IgG positivity; mRNA SARS‐CoV‐2 vaccine; self‐controlled case series study; vaccine safety.
This study investigated whether mRNA COVID‐19 vaccines might be linked to a rare neurological condition called MOG antibody‐associated disease (MOGAD), which can cause inflammation of the brain and spinal cord. Reports from individual patients have suggested a possible connection, prompting the current study of health data from nearly 6 million people in Denmark who were eligible for COVID‐19 vaccination. We identified 111 people who tested positive for MOG antibodies during the study period (i.e., 1 November 2020 to 31 December 2023), including 28 children. We compared how often these positive tests occurred shortly after vaccination versus other time periods. No increased risk was found in adults, but a possible increased risk was observed in children under 18 years old, although this was based on very small numbers. If the vaccine truly caused these cases, we estimated it would result in approximately four extra cases per 1 million vaccinated children. More research is needed to confirm these findings, but even if the association is real, the additional risk in children is very small.
© 2026 The Author(s). Pharmacoepidemiology and Drug Safety published by John Wiley & Sons Ltd.