Study Finds Reoccurrence of Adverse Events After Immunization is Relatively Low

If patients experienced an adverse event after vaccination, the likelihood that they would experience that adverse event again in subsequent doses of the vaccine was generally low, according to a new literature analysis study published in Pediatrics.

"The good news, if I may say, is what we see that has been published is giving us rates of recurrence that are not too high," Dr. Gaston De Serres, in charge of vaccine safety in research settings for the Quebec National Institute of Public Health, told Drug Topics. He is one of the study's investigators.

According to the findings of the analysis-which pooled results from 29 different articles-patients who had previously had a hypotonic hyporesponsive episode, anaphylaxis, or seizures and who were reimmunized had events occur in just 0% or 0.8% of cases. Adverse events that were described as "allergic-like" reoccurred in 30 of the 594 reimmunized patients.

The recurrence of other more minor adverse events, such as fever, were more common. The recurrence of a fever ranged from 0% to 84% in the 836 patients reimmunized, depending on the type of vaccine as well as the dose number.

"I think the message for most physicians and parents is to say, ‘Okay there is nothing really alarming in what we found’ and I think in most situations the physician will say to parents, ‘I think it's adequate to continue vaccinating the child given what has happened in the past visit,’" De Serres said.

De Serres and his colleagues wanted to examine the issue because reoccurrence of an adverse event can often be a significant worry for parents who are considering whether to continue with the next dose of a given vaccine.

While the literature review of the evidence available was relatively positive, De Serres also noted that there is a significant lack of scientific literature that has examined reoccurrence rates of adverse events following immunization.

"The number studies looking at this issue is very limited. There have been studies published where they pooled together high fever for all vaccines and it may not be appropriate," De Serres said. Some vaccines may be associated with higher rates of fever than others, he added.

Certain vaccines, such as the pertussis vaccine, may also be made by several different manufacturers. It is assumed that the various versions of a vaccine are comparable in terms of adverse events; however, scientific literature is lacking to confirm this, De Serres said.

According to the analysis, another challenge for literature studies is that patients who experienced severe adverse events are often not reimmunized, making it difficult to assess the adverse event rates in these cases.

De Serres hopes this literature review highlights the need within the scientific community to record and report the risk of reoccurrence for those who do experience adverse events, as a regular part of clinical trials examining the use of vaccinations.