Febrile Seizures Risk Compared With Inactivated Flu Vaccine, PCV13

Researchers assessed the risk of febrile seizures following inactivated influenza vaccine and pneumococcal conjugate vaccine-13 during 2013-14 and 2014-15 flu seasons.

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SAN DIEGO—Children faced an elevated risk of febrile seizures after receiving 13-valent pneumococcal conjugate vaccine (PCV13) but not inactivated influenza vaccine (IIV), according to findings from the Sentinel Initiative presented at IDWeek 2017. The authors’ analysis was statistically adjusted for concomitant administration of the other vaccine, the authors noted.

“The evidence suggests that concomitant administration of IIV with PCV13 might interact to increase the risk beyond the independent effects of PCV13, but the study was not powered to assess this interaction,” cautioned lead study author Meghan Baker, MD, ScD, from the Harvard Pilgrim Health Care Institute and Harvard Medical School, Boston, MA. 

Current data on the risk of febrile seizures post-vaccination with PCV13 and IIV is “mixed,” Dr. Baker noted. The research team sought to assess the risk of febrile seizures associated with these vaccines among patients aged 6–23 months for the 2013/14 and 2014/15 influenza seasons. Vaccine virus strains were the same for these seasons, they noted.

Claims data were acquired from 4 large national insurers in the FDA-sponsored Sentinel Initiative, which was developed to monitor the safety of FDA-regulated medical products. Dr. Baker and her team compared the risk of febrile seizures for 1 day after IIV and PCV13 with a comparison interval (Days 14 to 20). 

The authors adjusted for potentially confounding variables such as age and concomitant vaccination with the other vaccine. An exploratory analysis was also undertaken to assess whether the effect of IIV was impacted by concomitant PCV13 administration.  

The study period included 355,486 children who received IIV and 581,868 children who received PCV13. An incidence rate ratio (IRR) of 1.12 (95% CI: 0.80–1.56) was seen for the risk of febrile seizures following IIV after adjusting for the confounding factors. 

The IRR for PCV13 was 1.80 (95% CI: 1.29–2.52) after adjusting for confounding factors. “The attributable risk for PCV13 ranged from 0.33 to 5.16 per 100,000 doses,” noted Dr. Baker.

The test for interaction between IIV and PCV13 was not statistically significant, however (P=0.10, n.s.).

“The age and calendar-time adjusted IRR comparing exposed time to unexposed time was [numerically] greater for concomitant IIV and PCV13 (IRR 2.80, 95% CI: 1.63–4.83), as compared to that for PCV13 without concomitant IIV (IRR 1.54, 95% CI: 1.04–2.28),” Dr. Baker reported.  

Dr. Baker and coauthors concluded an “elevated risk of febrile seizures after PCV13 vaccine but not after IIV, when adjusting for concomitant administration of the other vaccine.” Some data suggested concomitant administration may increase the risk more than the separate effects of PCV13. 

“Risk of seizures associated with PCV13 is low compared to a child’s lifetime risk of febrile seizure,” emphasized Dr. Baker. “Findings should be interpreted in the context of the importance of preventing influenza and pneumococcal infections in young children.” 

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Baker, M. The Risk of Febrile Seizures Following Influenza and 13-Valent Pneumococcal Conjugate Vaccines. Poster presented at IDWeek; October 4–8, 2017; San Diego, CA. http://www.idweek.org