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Rate of Recurrence of Adverse Events Following Immunization

Results of 19 Years of Surveillance In Quebec, Canada

Zafack, Joseline G. MD*; Toth, Eveline Msc; Landry, Monique MD; Drolet, Jean-Philippe MD; Top, Karina A. MD§,¶,‖; De Serres, Gaston MD*,‡,**

The Pediatric Infectious Disease Journal: April 2019 - Volume 38 - Issue 4 - p 377–383
doi: 10.1097/INF.0000000000002162
Original Studies

Background: While adverse events following immunization (AEFI) are frequent, there are limited data on the safety of reimmunizing patients who had a prior AEFI. Our objective was to estimate the rate and severity of AEFI recurrences.

Methods: We analyzed data from the AEFI passive surveillance system in Quebec, Canada, that collects information on reimmunization of patients who had a prior AEFI. Patients with an initial AEFI reported to the surveillance system between 1998 and 2016 were included. Rate of AEFI recurrence was calculated as number of patients with recurrence/total number of patients reimmunized.

Results: Overall, 1350 patients were reimmunized, of which 59% were 2 years of age or younger. The AEFI recurred in 16% (215/1350) of patients, of whom 18% (42/215) rated the recurrence as more severe than the initial AEFI. Large local reactions extending beyond the nearest joint and lasting 4 days or more had the highest recurrence rate (67%, 6/9). Patients with hypotonic hyporesponsive episodes had the lowest rate of recurrence (2%, 1/50). Allergic-like events recurred in 12% (76/659) of patients, but none developed anaphylaxis. Of 33 patients with seizures following measles mumps rubella with/without varicella vaccine, none had a recurrence. Compared with patients with nonserious AEFIs, those with serious AEFIs were less often reimmunized (60% versus 80%; rate ratio: 0.8; 95% confidence interval: 0.66–0.86).

Conclusions: Most patients with a history of mild or moderate AEFI can be safely reimmunized. Additional studies are needed in patients with serious AEFIs who are less likely to be reimmunized.

From the *Department of Social and Preventive Medicine, Laval University, Quebec, Canada

Ministère de la santé et des services sociaux du Québec, Québec, Canada

CHU de Québec - Université Laval, Québec, Canada

§Department of Pediatrics

Department of Community Health and Epidemiology, Dalhousie University, Halifax, Canada

Canadian Center for Vaccinology, IWK Health Centre, Nova Scotia, Canada

**Direction des risques biologiques et occupationnels, Institut National de Santé Publique du Québec, Québec, Canada.

Accepted for publication July 10, 2018.

J.G.Z., G.D.S., E.T. and M.L. had full access to all of the data in the study and take responsibility for the integrity of the data and the accuracy of the data analysis.

This study was funded by the Ministère de la santé et des Services sociaux du Québec and by l’Institut national de santé publique du Québec. J.G.Z. received a PhD scholarship from the Canadian Immunization Research Network (CIRN), which is sponsored by the Public Health Agency of Canada and the Canadian Institutes of Health Research.

G.D.S. has received investigator initiated grants from GlaxoSmithKline and Pfizer. K.A.T. has received in-kind research support from Pfizer and research grant from GlaxoSmithKline. The other authors have no conflicts of interest to disclose.

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Address for correspondence: Gaston De Serres, MD, PhD, Direction des risques biologiques et occupationnels, Institut national de santé publique du Québec, 2400 Avenue d’Estimauville, Quebec city, Quebec, G1E 7G9, Canada. E-mail:

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