Rate of febrile seizures after flu vaccination similar to other childhood vaccines

The risk for febrile seizures after trivalent inactivated influenza vaccine is lower than originally estimated, according to data presented today during the Advisory Committee on Immunization Practices meeting.

Data from August to February of children aged 6 to 59 months who received a first dose of TIV plus other vaccines indicated that those children appeared to have an increased risk for febrile seizure.

However, Jeffrey Duchin, MD, chair of the ACIP working group on febrile seizures, said after reviewing the available data, the working group determined no change in practice is recommended at this time.

Jeffrey Duchin

“The bottom line is that based on the small number of seizures upon which the increased risk calculation is based, the absolute level of risk compared with other vaccines, and the substantial benefits of on-time vaccination with TIV and PCV [13-valent pneumococcal conjugate vaccine, Wyeth], no change in practice is recommended. The level of risk is comparable to that of other vaccines,” said Duchin, who is chief of communicable disease epidemiology and immunization at Seattle and King County Department of Public Health, and associate professor in medicine in the division of infectious diseases at the University of Washington.

Earlier this year, officials with the FDA and the CDC noted an increase in reports of febrile seizures among young children who received TIV (Fluzone) made by Sanofi-Pasteur. Fluzone was the only vaccine approved for children aged 6 to 23 months for the 2010-2011 influenza season, according to a statement issued by the FDA.

Risk for seizures

Jerome I. Tokars, MD, MPH, of the CDC’s National Center for Emerging and Zoonotic Infectious Diseases, told the committee that there was a slight elevated risk for febrile seizures after administration of last year’s formulation of TIV plus concomitant PCV13 and DTaP, but that the risk is neither statistically significant nor clinically important. The updated but still preliminary data suggest that the highest risk appeared in children aged 12 to 23 months, at a rate of 61 per 100,000 vaccinees, according to Tokars.

“We would like to know the risk of TIV given concomitantly vs. TIV given alone,” Tokars said, adding that this data is currently unavailable. A comprehensive study is planned, and results are expected early next year.

So far, the data indicate that the risk for febrile seizures with TIV was primarily present in the 2010-2011 season. The risk appeared to be highest when TIV was given with other vaccines, and concomitant PCV13 vs. DTaP was received equally by the cases reviewed. Data on DTaP are currently unavailable for evaluation. However, Tokars told committee members that PCV13 was new for the 2010-2011 influenza season and an increased risk for febrile seizures was not found after TIV in prior years when DTaP was used.

The updated estimate on attributable risk for children aged 12 to 23 months for TIV plus PCV13 is 42 per 100,000 (95% CI), Tokars said. The effect of a first dose vs. a second dose of TIV remains unknown. The ability to compare effects is limited because there were few second-dose vaccinees and few cases of febrile seizures.

Caveats to this data include: 1) TIV plus PCV13 concomitantly was measured vs. no vaccine, rather than TIV and PCV given at separate visits; and 2) the CI is wide and focused on a single-point risk estimate and could be misleading, according to Tokars.

Stay positive

Andrew Kroger, MD, MPH, of the CDC’s Education, Information & Partnership Branch in the National Center for Immunization and Respiratory Diseases, presented ideas to ACIP members on how to share this information with physicians and parents. Options could include adding the information as an ACIP policy note, adding the information to the Vaccine Information Statement or posting on the CDC website.

Kroger also discussed whether to recommend deferring some vaccines in the series as a way to lessen the risk for seizure. He asked the committee to consider the following: “Is there a family history or other indication? Should antipyretics be prescribed before or after vaccination? Should you ask about risk for invasive disease? Should there be additional criteria which must be met to make the decision to give simultaneous vaccinations or to defer?”

Committee member Mark H. Sawyer, MD, professor of pediatrics at the University of California, San Diego, said not to focus on the adverse events but rather the positive effects of immunization because it is already a struggle to make sure children receive the complete series of recommended vaccines.

“We run the risk of contributing to the already present lack of full immunization if we stress too much on adverse events,” Sawyer said.

Committee Chair Carol Baker, MD, agreed: “The risk of disease is much greater than the risk of this adverse event.” – by Cassandra A. Richards

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