CDC explores pneumococcal vaccine link to kids' febrile seizures

Feb 23, 2011 (CIDRAP News) – In their ongoing investigation of febrile seizures in young children who were vaccinated against flu this season, experts from the US Centers for Disease Control and Prevention (CDC) said today that they have detected a small excess risk of the condition in those who received the vaccine alongside the new pneumococcal conjugate vaccine.

The CDC enhanced its surveillance for febrile seizures in children who received the flu vaccine this season after Australia and New Zealand found higher-than-expected rates of fever and convulsions after flu immunization, mainly with Fluvax, made by CSL Ltd, in children younger than age 5.

In the United States, Sanofi's Fluzone is the only flu vaccine recommended this season for infants and children ages 6 to 23 months. On Jan 20 the CDC announced that it had detected an increase in the number of febrile seizures in children younger than 2 after Fluzone vaccination through its Vaccine Adverse Event Reporting System (VAERS).

At a meeting today of the CDC's Advisory Committee for Immunization Practices (ACIP), Grace Lee, MD, MPH, who leads the CDC's Vaccine Safety Datalink (VSD) studies, presented the latest preliminary findings from the group's investigation into the febrile illnesses.

She said rapid cycle analysis gives an almost real-time look at data collected through the VSD system, which includes medical visit data from 10 managed care organizations across the country, covering 9.2 million Americans, including 2.2 million children. Lee is a pediatrician at Harvard Medical School and Harvard Pilgrim Health Care Institute.

In late December scientists found signal for febrile seizures only in children ages 12 to 23 months who received the flu vaccine at the same time as the new pneumococcal conjugate vaccine. Lee told ACIP members that the excess risk was small and not statistically significant, but that VSD experts will continue to probe the connection.

She said a review from past seasons of children who received the flu vaccine with other childhood immunizations did not detect the unique signal.

Lee said the group can't rule out the possible contribution of other concomitant vaccines that the children received and said researchers will also explore the role of other possible confounders.

In February 2010 the ACIP recommended that children under age 5 receive the newer pneumococcal conjugate vaccine (PCV13) that covers against a broader range of strains than the earlier PCV7 version, according to an ACIP report that was published in the March 12, 2010, issue of Morbidity and Mortality Weekly Report (MMWR). The four-dose series is given at 2, 4, 6, and between 12 and 15 months. PCV13 is made by Wyeth, a subsidiary of Pfizer.

She said the next steps are to continue monitoring the data so that the group can prepare an end-of-season report on its findings.

ACIP members did not change their flu vaccine recommendations for children based on the new information, but they agreed that the possible febrile seizure link to the vaccines needed further study.

Febrile seizures can result from high body temperatures and several common childhood infections such as colds, ear infections, and flu, and in rare instances can occur after vaccination. A 2006 New England Journal of Medicine study estimated febrile seizures occur in 1% of children under age 5 with lab-confirmed influenza and in 9% of kids who are hospitalized with flu.

CDC background information said febrile seizures in children aren't uncommon, and about 2% to 5% will have at least one. Most occur between ages 6 months and 5 years, with a peak age of 14 to 18 months. Though febrile seizures can be frightening, nearly all children who have them recover quickly with no long-term effects.

See also:

Jan 21 CIDRAP News story "Feds probe possible febrile seizure link to Sanofi flu vaccine"

Mar 10, 2010, MMWR report

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