Layton JB, Mayer SE, Praet N, Haynes K, Alam S, Brown JS, Calingaert B, Daniels K, Dea K, DeVries A, Diessner B, Djibo DA, Hague JC, Horgan C, Hugh C, Johannes CB, Ko J, Love S-AM, Ma Q, McMahill-Walraven CN, Moyneur E, Platt R, Selvan M, Wang X, Yost E, Ziyadeh NJ, Fuller CC, Gilsenan A. An observational postauthorization safety study to assess adverse events of special interest in recipients of Ad26.COV2.S in the United States. Presented at the 2025 International Society for Pharmacoepidemiology (ISPE) Annual Meeting; August 26, 2025. Washington, DC.

BACKGROUND: Ad26.COV2.S was a monovalent COVID-19 vaccine granted emergency use authorization (EUA) in the US from February 2021 to June 2023. Warnings of adverse events in the EUA prescribing information as of March 2023 included anaphylaxis, co-occurring thrombosis with thrombocytopenia syndrome (TTS), immune thrombocytopenia (ITP), Guillain-Barré Syndrome (GBS), and myocarditis/pericarditis. A US postauthorization safety study (PASS) evaluated the association of Ad26.COV2.S with these and other adverse events of special interest (AESIs).

OBJECTIVES: To assess the potential association between the occurrence of the aforementioned AESIs and vaccination with Ad26.COV2.S within disease-specific risk periods in adults aged 18 years and older.

METHODS: A self-controlled risk interval (SCRI) analysis identified adults who received Ad26.COV2.S as their first-ever COVID-19 vaccine between 27 February 2021 and 31 December 2021. Data from 4 US health insurance data sources participating in the FDA’s Sentinel System were used; immunization information system vaccination records also were included, when available. AESI-specific postvaccination risk and control periods (3, 21, 28, or 42 days) were defined within each vaccinated individual; enrollment was required from at least 1 year before vaccination to the end of the control period or death. AESI-specific analysis sets comprised those with an AESI in the risk or control period who were free of occurrences of the AESI within AESI-specific washout periods before the event. Relative incidence ratios (RIRs) and 95% confidence intervals (CIs) comparing AESI incidence during the risk and control periods were estimated using conditional Poisson regression. Sensitivity and subgroup analyses (e.g., by age and sex) were also performed.

RESULTS: Across all data sources, we identified 419,647 eligible Ad26.COV2.S recipients. Pooled RIRs and total sample sizes from AESI-specific analysis sets were anaphylaxis (RIR, 1.14; 95% CI, 0.36-3.70; N=15); TTS (RIR, 1.82; 95% CI, 1.27-2.63; N=138); ITP (RIR, 1.00; 95% CI, 0.54-1.84; N=48); GBS (RIR, 2.50; 95% CI, 0.41-26.25; N=7), and myocarditis/pericarditis (RIR, 1.33; 95% CI, 0.69-2.61; N=42). Sensitivity and subgroup analyses were generally consistent with the overall estimates; for myocarditis/pericarditis, differences were seen by age and sex, with the largest RIR (6.00) observed in men aged 18-39 years (95% CI, 0.73-275.99; N=7).

CONCLUSIONS: Though some estimates were imprecise due to small case counts, we observed RIR estimates in this PASS for anaphylaxis, TTS, GBS, and myocarditis/pericarditis that were consistent with the warnings in the EUA prescribing information. For ITP, the PASS results did not suggest an increased risk associated with Ad26.COV2.S.