MONDAY, Sept. 24, 2018 -- Most children who have mild to moderate reactions to a vaccine can safely receive booster shots, new research suggests.
Canadian scientists found there is a low rate of recurring reactions following subsequent vaccinations. They said their findings should help inform doctors and parents about the safety of immunizations.
"Most patients with a history of mild or moderate adverse events following immunization can be safely re-immunized," said study leader Dr. Gaston De Serres, of Laval University in Quebec.
In the United States, health care professionals are legally required to report reactions to immunizations. Quebec has a similar reporting system for "unusual or severe" vaccine reactions.
For the study, De Serres and colleagues analyzed data on 5,600 patients in this Canadian database from 1998 to 2016. All required additional doses of a vaccine that caused them to have a reaction. The researchers noted the seasonal flu shot was not included in the study since this vaccine changes from year to year.
Follow-up data was available on 1,731 of these patients. Of these, 78 percent, or 1,350 people, received an additional vaccination. In most cases, the patients who received booster shots were younger than 2.
The study found that only 16 percent of the patients had another reaction after receiving an additional vaccination. The researchers also found that more than 80 percent of these subsequent reactions were not any more severe than the initial reaction. Patients' gender didn't affect the rate of reactions.
The findings were published recently in The Pediatric Infectious Disease Journal.
In a journal news release, the research team identified a few patterns related to vaccine reactions, including:
- Older age. Kids younger than 2 were more likely to be revaccinated and less likely to have more than one reaction than older patients.
- Type of reaction. Patients with large, local reactions that result in severe swelling of the affected limb had the highest rate of future reactions. The reaction recurrence rate was 67 percent for these patients, compared to 12 percent among those who had allergic-type reactions. Severe reactions (anaphylaxis) following subsequent vaccinations were very rare.
- Severity of reaction. The study showed that 60 percent of patients who had the most severe initial reactions were revaccinated. The same was true for 80 percent of those who had more moderate reactions. Of the patients who had severe initial reactions, however, only 8 percent experienced a recurrence when they received another immunization. Meanwhile, 17 percent of the patients who had mild reactions had a subsequent reaction.
- Type of vaccine. Reaction recurrence rates didn't vary much for different types of vaccines. But the researchers did find that revaccination following a reaction was highest among children who received a diphtheria-tetanus-pertussis (DTaP) vaccine.
The U.S. Centers for Disease Control and Prevention provides more information on vaccines and immunizations.
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