Revaccination and Adverse Event Recurrence in Patients with Adverse Events following Immunization.

To estimate the risk of recurrence of adverse events following immunization (AEFIs) upon revaccination and to determine among patients with suspected vaccine allergy whether allergy skin test positivity was associated with AEFI recurrence. This prospective observational study included patients assessed in the Canadian Special Immunization Clinic Network from 2013 to 2019 with AEFIs who required revaccination with the vaccine temporally associated with their AEFI. Participants underwent standardized assessment and data collection. Special Immunization Clinic physicians used guidelines to inform their recommendations. Participants were followed up after revaccination to capture AEFI recurrences. Data were transferred to a central database for descriptive analysis. Overall, 588 participants were assessed for 627 AEFIs; 570 (91%) AEFIs occurred in children <18 years of age. AEFIs included immediate hypersensitivity (130/627; 21%), large local reactions (110/627; 18%), nonurticarial rash (51/627; 8%), seizures (26/627; 4%), and thrombocytopenia (11/627; 2%). Revaccination was recommended to 513 of 588 (87%) participants. Among participants recommended and due for revaccination during the study period, 63% (299/477) were revaccinated. AEFI recurrence was 10% (31/299) overall, 31% (15/49) for large local reactions, and 7% (5/66) for immediate hypersensitivity. No recurrence was serious. Among 92 participants with suspected vaccine allergy who underwent skin testing and were revaccinated, the negative predictive value of skin testing for AEFI recurrence was 96% (95% CI 92.5%-99.5%). Most individuals with AEFIs were safely revaccinated. Among those with suspected vaccine allergy, skin testing may help determine the safety of revaccination.

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