Repeat vaccination is safe for most kids with mild to moderate reactions

Children with a history of mild or moderate adverse events following immunization (AEFI) can be safely reimmunized, reports a study published in The Pediatric Infectious Disease Journal.

"Most patients with a history of mild or moderate adverse events following immunization [AEFI] can be safely reimmunized," write Gaston De Serres, MD, of Laval University, Quebec, and colleagues. Although recurrent AEFIs can sometimes occur after repeat doses of vaccine, this study suggests that the risk of recurrent AEFIs after re-vaccination is relatively low, especially when the previous reaction was mild or moderate.

While adverse events following immunization (AEFI) are frequent, there are limited data on the safety of reimmunizing patients who had a prior AEFI. Zafack and associates conducted a study to estimate the rate and severity of AEFI recurrences.

The analysis included 5,600 patients with AEFIs reported to Quebec's passive surveillance database from 1998 through 2016, all of whom required further doses of the vaccine to which they reacted. (The analysis excluded seasonal influenza vaccine, which changes from year to year.)

Of 1,731 patients with available follow-up data, 1,350 patients were re-vaccinated: a rate of 78 percent. Most of the re-vaccinated children were under two years old; about one-half of the AEFIs were allergic-like reactions.

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Key study findings:

• The AEFI recurred in 16% (215/1350) of patients, of whom 18% (42/215) rated the recurrence 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 non-serious AEFIs, those with serious AEFIs were less often reimmunized (60% versus 80%, rate ratio: 0.8, 95% confidence interval 0.66 to 0.86).

The study is one of the largest to estimate the rate of recurrent AEFIs by type of reaction and type of vaccine - key information for healthcare providers and parents/caregivers making decisions about further immunization. The results support the safety of continued vaccination especially when the previous reaction was mild or moderate.

The study concluded that children who experience some type of adverse event following initial immunization have a low rate of recurrent reactions to subsequent vaccinations.