New‐onset autoimmune disease following SARS‐CoV‐2 infection and mRNA vaccination in Norway: A retrospective cohort study

Abstract Background Studies suggest an increase in autoimmune diseases following SARS‐CoV‐2 infection and/or COVID‐19‐vaccination. We aimed to describe possible associations in Norway. Methods We used information from the emergency preparedness register for COVID‐19, BeredtC19, for all residents aged 18–64 ( N = 3,450,080). BeredtC19 includes data from mandatory nationwide registers on demographics, SARS‐CoV‐2 tests, deaths, vaccinations, and hospitalizations. Cox regression was used to estimate adjusted hazard ratios (aHRs) for 30‐day and 30–180 day risk windows. Findings SARS‐CoV‐2 infection was associated with an increased risk of purpura, thrombocytopenia, and agranulocytosis within 30 days and 30–180 days. In the first 30 days, Bell's palsy and inflammatory arthritis were associated with infection, whereas 30–180 days postinfection showed an association with polyneuropathy. Vaccination was associated with an increased risk of inflammatory bowel disease (IBD) and celiac disease, both in the first 30 days and 30–180 days postvaccination. Additionally, in the first 30 days postvaccination, we found associations with inflammatory arthritis and erythema nodosum, and between 30 and 180 days with arthralgia, agranulocytosis, and acute disseminated encephalomyelitis (ADEM). There was also a reduced risk of dermatopolymyositis 30–180 days postvaccination. Interpretation Most autoimmune disorders showed no significant association with SARS‐CoV‐2 infection or COVID‐19 vaccination. Associations between vaccination and IBD and ADEM warrant further investigations, as these observations reflect associations and do not establish causality.