BACKGROUND: In fall 2010 in the Southern Hemisphere, increased risk of febrile seizures was noted in young children in Australia in the 24 hours after trivalent inactivated influenza vaccine (TIV) manufactured by CSL Biotherapies.
OBJECTIVES: During the 2010–2011 season, weekly surveillance was conducted for febrile seizures in the 0–1 days following first dose TIV in 206,174 children ages 6–59 months in the Vaccine Safety Datalink, a collaboration between the Centers for Disease Control and Prevention and 10 medical care organizations.
METHODS: Weekly surveillance was conducted with self-controlled risk interval and current vs. historical vaccineedesigns. Sequential statistical methods were used to account for repeated analyses. Signals for seizures based on computerized data were identified in mid November2010 with the current vs. historical design and in late December 2010 with the self-controlled risk interval design. Signal evaluation was conducted with chart-con-firmed febrile seizure cases using the self -controlled risk interval design.
RESULTS: The incidence rate ratio (IRR) for TIV adjusted for concomitant 13-valent pneumococcal conjugate vac-cine (PCV13) was 2.4 (95% CI 1.2, 4.7) while the IRR forPCV13 adjusted for concomitant TIV was 2.5 (95% CI1.3, 4.7). The risk differences (RD) varied by age and receipt of concomitant PCV13, with the highest estimates at 16 months (13 per 100,000 doses for TIV without concomitant PCV13, 14 per 100,000 doses for PCV13 without concomitant TIV, and 45 per 100,000 doses for concomitant TIV and PCV13) and the lowest estimates at59 months (one per 100,000 doses for TIV without concomitant PCV13, one per 100,000 doses for PCV13 without concomitant TIV, and four per 100,000 doses for concomitant TIV and PCV13).
CONCLUSIONS: An elevated risk of febrile seizures in the 0–1 days following first dose TIV was identified during t he2010–2011 season in children ages 6–59 months. The magnitude of RD estimates was dependent on age and concomitant PCV13 vaccine, with the highest RDs at16 months and the lowest RDs at 59 months. Resultsshould be placed in a benefit-risk framework to maximize population health benefits.
