Febrile Seizure Risk After Vaccination in Children 6 to 23 Months

Abstract

Background and objective: An increased risk of febrile seizure (FS) was identified with concomitant administration of trivalent inactivated influenza vaccine (IIV3) and pneumococcal conjugate vaccine (PCV) 13-valent during the 2010-2011 influenza season. Our objective was to determine whether concomitant administration of IIV3 with other vaccines affects the FS risk.

Methods: We examined the risk of FS 0 to 1 day postvaccination for all routinely recommended vaccines among children aged 6 through 23 months during a period encompassing 5 influenza seasons (2006-2007 through 2010-2011). We used a population-based self-controlled risk interval analysis with a control interval of 14 to 20 days postvaccination. We used multivariable regression to control for receipt of concomitant vaccines and test for interaction between vaccines.

Results: Only PCV 7-valent had an independent FS risk (incidence rate ratio [IRR], 1.98; 95% confidence interval [CI], 1.00 to 3.91). IIV3 had no independent risk (IRR, 0.46; 95% CI, 0.21 to 1.02), but risk was increased when IIV3 was given with either PCV (IRR, 3.50; 95% CI, 1.13 to 10.85) or a diphtheria-tetanus-acellular-pertussis (DTaP)-containing vaccine (IRR, 3.50; 95% CI, 1.52 to 8.07). The maximum estimated absolute excess risk due to concomitant administration of IIV3, PCV, and DTaP-containing vaccines compared with administration on separate days was 30 FS per 100 000 persons vaccinated.

Conclusions: The administration of IIV3 on the same day as either PCV or a DTaP-containing vaccine was associated with a greater risk of FS than when IIV3 was given on a separate day. The absolute risk of postvaccination FS with these vaccine combinations was small.

FIGURE 1

Comparison of the estimated AR of FS associated with each unique combination of IIV3, PCV, and DTaP-containing vaccines when administered on separate days or together The AR estimates shown are for vaccine administration at 15 months of age. The x-axis denotes the vaccine or vaccine combination (indicated by a + between vaccine names). The total height of each column represents the AR for the vaccine or vaccine combination named on the x-axis. The individual blocks within each column indicate the estimated portion of the total risk that would be expected to be contributed by each individual vaccine (eg, PCV) or the excess risk contributed by the interaction between ≥2 vaccines (as indicated by a * [eg, IIV3*DTaP]). The AR for IIV3 or DTaP given alone is each 0. In this figure, the notation “DTaP” refers to any of the different types of DTaP-containing vaccines; “PCV” refers to either PCV7 or PCV13.