Abstract
Background Post-marketing surveillance monitors reports of adverse events following vaccination, including reports of hepatitis. The Vaccine Adverse Event Reporting System (VAERS) is a passive surveillance system that can describe reporting patterns but cannot establish incidence, risk, or causality. This study aimed to characterize hepatitis reports received by VAERS based upon demographic characteristics, vaccine types, onset intervals, reported outcomes, seriousness classification, and temporal patterns in reporting. Methodology Data for this study were collected via a retrospective, cross-sectional analysis utilizing the Centers for Disease Control and Prevention's Wide-ranging Online Data for Epidemiologic Research VAERS database. Reports of "Hepatitis" as the Medical Dictionary for Regulatory Activities (MedDRA) Preferred Term (code 10019717) were extracted from data that had been processed through April 24, 2026. Data for 2026 were partial because the database had been processed only through April 24, 2026. For reports where the reporting year could be determined, the time frame was 1990 to 2026. Data were categorized into frequency distributions and percentages for categorical variables. Pearson's chi-square tests were conducted to compare serious vs. non-serious reports by age group, sex reported, and onset interval. Cramér's V was calculated to quantify the magnitude of the differences between the groups. Due to the lack of mutual exclusivity among the categories for vaccine types and therefore the inability to treat them as independent data points, summary statistics describing the results for vaccine type were generated. Results A total of 529 hepatitis reports were retrieved. Of these 529 reports, 200 (37.81%) were designated as serious reports, while 329 (62.19%) were designated as non-serious reports. Individuals between the ages of 18 and 49 years comprised the greatest number of reports (n = 216; 40.83%). The female sex was identified in 261 (49.34%) reports. In 178 (33.65%) reports, the onset interval was unknown. Among those reports that documented an onset interval, one to three days was the most frequently documented onset interval (n = 70; 13.23% of all reports). Hepatitis B vaccines (n = 267; 50.47%) and COVID-19 vaccines (n = 134; 25.33%) were the two vaccine types most frequently documented. The seriousness classification was significantly different among the various age categories (χ²(5) = 21.61, p = 0.0006; Cramér's V = 0.224). Neither sex (χ²(1) = 3.84, p = 0.0502; Cramér's V = 0.089) nor onset interval (χ²(7) = 8.88, p = 0.2614; Cramér's V = 0.159) were significantly related to seriousness classification. Vaccine-type findings were limited to descriptive comparisons because the categories were not mutually exclusive. Conclusions Reports of hepatitis that have been sent to the VAERS demonstrate differing classifications of seriousness based upon the age group. The vaccine-type findings were presented as descriptive summaries, as each report may contain multiple vaccines. Results presented here represent only patterns found in reports received by the VAERS; they do not provide an estimate of vaccine-specific risk, incidence, or causation. Further investigation into these findings will require additional research using denominator-based and clinically validated data.