Vaccines and febrile seizure risk

Influenza and pneumococcal vaccines may cause febrile seizures when administered together, according to a new report, but the benefits of vaccination still outweigh the possible risks.

The report, published in Pediatrics, sought to determine whether administration of trivalent inactivated influenza vaccine (IIV3) alongside other vaccines would increase febrile seizure risk.

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The research team found that there was increased risk of febrile seizure on the day of vaccination and the day after when inactivated influenza vaccines were administered at the same time as the pneumococcal conjugate vaccine or a Diphtheria, Tetanus, and acellular Pertussis (DTaP) vaccine. The risk is small, says Jonathan Duffy, MD, MPH, a medical officer with the Centers for Disease Control and Prevention (CDC) in Atlanta, Georgia and lead author of the study, with no more than 30 febrile seizures per 100,000 children vaccinated, so the Advisory Committee on Immunization Practices has decided that the findings don’t warrant any changes in the current recommended use of these vaccines.

“These vaccines prevent infections that can sometimes be severe or life-threatening. The benefits of timely vaccination are likely much greater than the small risk of febrile seizure,” Duffy says. “Febrile seizures are relatively benign and do not cause lasting harm. Influenza vaccine, when needed, should still be given at the same time as these other vaccines.”

Duffy says he hopes his team’s research will, however, spur a discussion between pediatricians and parents about the benefits and risks of childhood vaccines. He says the study is also a reminder to pediatricians about risk of febrile seizure following inactivated vaccines, which is greatest in the first 24 hours.

The increased risk of febrile seizure was identified when IIV3 and pneumococcal conjugate vaccine 13-valent (PCV-13) were administered together during the 2010–2011 influenza season, according to the report. The team also found that only PCV-7 had an independent febrile seizure risk, but that there was also a risk with IIV3 when paired with PCV-7-valent or PCV-13.

Overall, the team determined that administration of IIV3 on the same day as any PCV or DTaP-containing vaccine may increase the risk of febrile seizure compared with when the vaccines are administered on separate days.

Febrile seizures occur in about 5% of children aged 6 to 60 months because of various infections such as influenza or after certain vaccines including diphtheria, tetanus toxoids, whole cell pertussis vaccine; measles, mumps, rubella vaccine (MMR); and varicella combination vaccine (MMRV), the report says.

“Previous studies have examined the risk of febrile seizure follow the live attenuated vaccines MMR and MMRV, and the greatest risk of febrile seizure with measles-containing vaccines occurs 7 to 10 days after vaccination,” Duffy says.

NEXT: Febrile seizure risk and IIV3 administration

No increased risk of febrile seizure was observed after IIV3 administration prior to 2010, when an Australian report revealed increased febrile seizure risk in a particular IIV3 brand 12 hours after administration. Follow-up studies in the United States confirmed increased risk of febrile seizure with IIV3 vaccination, according to the report, although it was theorized that the PCV13 introduced the same year may have played a role in the febrile seizure risk findings in the United States. Later studies confirmed independent febrile seizure risks for both the IIV3 and PCV13 vaccines, with the greatest risk occurring when the 2 vaccines were administered together.

The research team also notes that febrile seizure risks related to the IIV3 vaccine varied based on the season. The vaccine includes 3 different influenza virus strains that are changed nearly every year to customize it for the influenza viruses expected during that flu season.

Because of the low absolute risk, the research team notes that the risk may be outweighed by the benefits of timely vaccination that can be achieved by giving IIV3 vaccines on the same day as others when needed.

NEXT: What parents want to know about vaccinations

Neither parents nor children typically look forward to vaccinations, and cost or transportation may be an issue in achieving compliance in some cases. According to the CDC, many physicians avoid administering multiple vaccines at one time out of concern of adverse events or because of parental objection. Although concerns about adverse events are not supported by scientific data, CDC says this type of misinformation can lead to missed opportunities for vaccination. Eliminating missed opportunities could increase vaccination coverage by up to 20%, according to the CDC.

Although coverage rates among infants and young children are around 90% for most vaccines, fewer than half of all children received early season influenza vaccination in the 2015-16 season.

Roughly 30% of children who have 1 febrile seizure will have more, researchers add, and whereas there are several risk factors for recurring febrile seizures, there are no evidence-based strategies for risk reduction. Giving prophylactic antipyretics is not recommended, and oral diazepam given at the onset of febrile illness may be effective in preventing recurrence but is not recommended because of the potential adverse effects, according to the report.

More research is needed to determine possible evidence-based strategies to reduce short-term, postvaccination febrile seizure risks, the researchers say.