Acute autoimmune hepatitis following COVID-19 mRNA vaccination: A population-based study using electronic health records in Singapore.

Reports of coronavirus disease 2019 (COVID-19) vaccine-induced autoimmune hepatitis (AIH) have been largely limited to case reports and case series. To further investigate the association between COVID-19 mRNA vaccination and AIH, we conducted a nationwide study using observed-over-expected (O/E) and Self-Controlled Case Series (SCCS) analyses for acute presentations of AIH (AAIH) warranting admission. Patients were included if they had one or more of the following hepatitis-related signs and symptoms (fever, lethargy, jaundice or abdominal pain) reported up to 3 months prior to admission, deranged liver function tests [alanine transaminase (ALT) or aspartate aminotransferase (AST) greater than three times the upper limit of laboratory reference ranges], as well as biopsy results characteristic of AIH or response to steroid treatment for cases which did not undergo biopsy. Seventy-six patients fulfilled our case definition of AAIH within the study period from 1 January 2019 to 28 February 2023, with 6 patients having an estimated onset of AAIH within 42 days of COVID-19 mRNA vaccination. All 6 patients were females aged 40 years and above. In the O/E analysis, the rate ratios of AAIH among females aged 40 years and above in the primary cohort were 1.12 (95% confidence interval (CI) 0.14-9.40) and 1.06 (95% CI 0.24-4.74) in the 21 days and 42 days following vaccination respectively. In the SCCS analysis, we did not observe any statistically significant increase in incidence of AAIH in the 21 and 42 days following COVID-19 mRNA vaccination for both the primary and supplementary cohorts, as well as in the subgroup analysis involving females aged 40 years and above. Our findings suggest that COVID-19 mRNA vaccination does not appear to be associated with increased risk of AAIH requiring admissions in the population, although larger studies are required to confirm these findings.