Only 16% of Patients Experienced Adverse Events After Re-vaccination

To continue the success of immunization programs, patient confidence in the safety of vaccines is mandatory.

Although immunizations are generally safe, adverse events following immunization (AEFI) do occur, and in rare cases, they may be serious.

A new study is reporting, children who experience some type of adverse event following initial immunization, have a low rate of recurrent reactions to additional vaccinations.

Only 16 percent of patients experienced some type of recurrent AEFI after re-vaccination.

Moreover, in more than 80 percent of cases, the recurrent reaction was no more severe than the initial reaction.  

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.

"Most patients with a history of mild or moderate adverse events following immunization can be safely reimmunized," said Gaston De Serres, MD, of Laval University, Quebec, in a press release. 

This 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 annually.

Of 1,731 patients with available follow-up data, 1,350 patients were re-vaccinated, which is a rate of 78 percent. Most of the re-vaccinated children were under 2 years old and about 50 percent of the AEFIs were allergic-like reactions.

The researchers analyzed potential risk factors for recurrent reactions, including:

• Patient Characteristics. Children under age 2 were more likely to be re-vaccinated and less likely to have recurrent reactions, compared to older patients. Recurrence risk was similar for males and females.
• Type of AEFI. The recurrence rate was similar for patients with most types of initial AEFIs. The risk was highest (67 percent) for patients with large local reactions with "extensive limb swelling." For patients who had allergic-type reactions, the recurrence rate was 12 percent. Severe allergic events (anaphylaxis) were very rare after re-vaccination.
• The severity of AEFI. Patients with more severe initial AEFIs were less likely to be re-vaccinated: only 60 percent of children with severe reactions were re-vaccinated, compared to 80 percent of those with less-severe reactions. Within this selected group, patients with severe AEFIs were less likely to have recurrences: eight versus 17 percent.
• Type of Vaccine. The recurrence rate did not differ significantly for different types of vaccines. The re-vaccination rate was highest (90 percent) for children with AEFIs to diphtheria-tetanus-pertussis vaccines.

This 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.

Dr. De Serres and coauthors suggest that vaccine adverse event passive surveillance systems could be adapted to include "systematic and standardized follow-up" to provide more complete information on recurrence risk and other outcomes for children with AEFIs.

In October 2017, the Advisory Committee on Immunization Practices (ACIP) approved the 2018 immunization schedule for children and adolescents birth through 18 years, effective February 2018.  

The schedule has been approved by the Centers for Disease Control and Prevention (CDC), the American Academy of Pediatrics (AAP), the American Academy of Family Physicians (AAFP), and the American College of Obstetricians and Gynecologists (ACOG).

The comprehensive summary of the ACIP recommended changes to the schedule can be found in the February 6, 2018 MMWR.

No conflicts of interest were disclosed by these researchers.