Evaluating the safety of XBB.1.5-containing COVID-19 mRNA vaccines using a self-controlled case series study.

The safety of XBB.1.5-containing COVID-19 mRNA vaccines warrants investigation. We assessed the relative risk of 15 adverse events following the XBB.1.5 vaccination using a self-controlled case series study design with data from the National COVID Cohort Collaborative (N3C) from September 11, 2023, to June 1, 2024 in the USA. Based on a baseline population of 244,494 patients, adverse events included Guillain-Barré syndrome, seizure, non-hemorrhagic stroke and transient ischemic attack, hemorrhagic stroke, narcolepsy or cataplexy, anaphylaxis, acute myocardial infarction, myo/pericarditis, coagulopathy, multisystem inflammatory syndrome, Bell's palsy, transverse myelitis, appendicitis, pulmonary embolism, and encephalitis. We found an association between vaccination and anaphylaxis (IRR [95% CI]: day 0-17.35 [9.32-30.03], day 1-9.35 [5.12-15.95], day 2-6.20 [3.40-10.57], <20 patients in each risk period). No other outcomes showed significantly increased risk following vaccination. Our results contribute to the safety profile evaluation for XBB.1.5-containing COVID-19 mRNA vaccines utilizing N3C big data.