1. Administration of inactivated influenza vaccination alone was not associated with an increased risk of febrile seizures.
2. Concomitant administration of pneumococcal or DTaP-containing vaccinations with inactivated influenza vaccine was associated with a slightly increased risk of febrile seizures.
Evidence Rating Level: 2 (Good)
Study Rundown: Some vaccinations, including diphtheria, tetanus, pertussis (DTaP) and measles, mumps and rubella (MMR), have previously been associated with a small increased risk of febrile seizure following administration. Prior to 2010, there was no noted increased risk of febrile seizure associated with inactivated influenza vaccination (IIV3). However, vaccine safety monitoring demonstrated an increased risk of febrile seizure with IIV3 administered concomitantly with the 13-valent pneumococcal vaccination (PCV13) after its introduction in 2010. Authors of this study sought to examine the risk of febrile seizure following the concomitant administration of IIV3 with other vaccinations. Results indicated that the risk of febrile seizure was increased when IIV3 was administered concomitantly with a PCV or DTaP-containing immunization, but not when IIV3 was administered alone. The increased risk was minimal when compared to administering the vaccinations on separate days. Limitations of this study included its retrospective design and reliance on vaccine safety reporting systems. Nonetheless, while the absolute risk increase was found to be minimal, physicians should participate in shared decision making about concomitant vaccine administration with parents.
In-Depth [cohort study]: A total of 1 914 108 vaccination events in 6 to 23-month old infants were identified at 10 CDC vaccine monitoring sites from 5 influenza seasons (2006 to 2011). 333 chart-confirmed cases of febrile seizure after vaccination at either day 0-1 or 14-20 were identified. They served as their own controls and the rate of febrile seizure during days 0-1 was compared to the rate at days 14-20. IIV3 alone was not associated with febrile seizure in any of the examined years (IRR*=0.46, CI 0.21-1.02). However, when IIV3 was administered concomitantly with PCV, the relative excess risk of FS was 2.23 (CI –0.87-12.76). When IIV3 was administered on the same day as a DTaP containing vaccine, the excess risk was 3.00 (CI 0.26-8.75).
*IRR: incidence rate ratio, the incidence rate of febrile seizure at day 0-1 over the incidence rate of febrile seizure at day 14-20
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