Reimmunization appears to be safe for patients with mild to moderate adverse events following immunization (AEFI), but there are not enough data to make firm conclusions about severe AEFIs, according to a systematic review of studies that were published in English and French between 1982 and 2016 and were made available to Medline via PubMed, Embase, and the Cochrane library.

The review, published in Pediatrics (2017 Aug. doi: 10.1542.peds.2016-3707 ), looked at 29 studies. Of those, eight collectively found that allergic-like events recurred in 30 of 594 patients (5%; 95% confidence interval, 3.3-6.8), Joseline Guetsop Zafack, MD, MPH, of the department of social and preventive medicine at Laval University in Quebec, and her coauthors reported. They noted that “recurrences did not dissuade patients from continuing immunization.” In the six studies that looked at recurrence of hypotonic-hyporesponsive episodes, only 3 of 398 patients had a recurrence (0.8%; 95% CI, 0.2-2.2). None of three studies found recurrence of seizure in children who were reimmunized..

Apnea was found to be of concern only in children under the age of 1 year and usually found only in lower birth weight babies and those with ongoing hospitalization for complications related to prematurity, the investigators said. A 10-g increase in birth weight was associated with a 6% reduction in risk of apnea recurrence (odds ratio, 0.94; 95% CI, 0.89-1.00), and odds of recurrence were 23 times higher in infants hospitalized for complications related to prematurity (OR, 23; 95% CI, 2-272).

Some of the studies also evaluated for injection site reactions, Henoch-Schönlein purpura, or other AEFI, Dr. Zafack and her coauthors continued. Injection site reactions varied depending on vaccine and number of doses, but all children recovered within 19 days of immunization. Only one child in one study had a recurrence of Henoch-Schönlein purpura. Vomiting, persistent crying, decreased appetite, and drowsiness recurred in 15%, 24%, 25%, and 35% of the reimmunized patients, respectively, across all the studies.

“In a context of vaccine hesitancy and growing concerns regarding vaccine safety, evaluating the risk of recurrence of all AEFIs should become part of the standard evaluation of vaccine safety,” the researchers wrote. “Reimmunization appears to be safe for patients with mild to moderate AEFIs. However, the data are insufficient to draw firm conclusions regarding the safety of reimmunization after a severe AEFI.”

In this study, “it appears that the risk of recurrence of serious AEFIs (anaphylaxis, seizures, or apnea in term infants) was low (less than 1%). For minor to moderate AEFIs (fever, extensive limb swelling, oculorespiratory syndrome, allergic-like events, sleepiness, thrombocytopenia, decreased appetite, vomiting, or persistent crying), the risk of recurrence ranged from 4% to 48%,” the investigators concluded.

The study was funded by the Canadian Immunization Research Network, which is sponsored by the Public Health Agency of Canada and the Canadian Institutes of Health Research. Dr. Zafack reported no financial disclosures. Some of her coauthors reported financial support from GlaxoSmithKline and Pfizer.


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