New information from the Vaccine Adverse Event Reporting System (VAERS) provides “generally reassuring, although limited” data on the safety of trivalent influenza vaccine administration to infants and toddlers younger than 2 years of age.

Because a number of seizures were apparently related to vaccination, “continued surveillance for seizures and other clinically significant adverse events is warranted and will continue,” write officials from the U.S. FDA and the Centers for Disease Control and Prevention in the journal Pediatrics.

In April 2002, the Advisory Committee on Immunization Practices (ACIP) encouraged healthcare providers to vaccinate healthy infants aged 6 to 23 months with the trivalent influenza vaccine. In October 2003, the committee recommended universal vaccination of this age group beginning with the 2004-2005 influenza season.

In their paper, Dr. Ann W. McMahon from the FDA’s Center for Biologics Evaluation and Research and colleagues describe adverse events reported to VAERS before the ACIP guideline (January 1990 to June 2002) and after (July 2002 to June 2003) “as a way of determining whether new adverse events would be detected in the new era.”

Between 1990 and 2003, VAERS received a total of 166 reports of adverse events after trivalent influenza vaccine administration in children younger than age 2, the investigators report. The majority of these (63 percent) occurred after administration of influenza vaccine plus one or more other vaccines.

The number of trivalent influenza vaccine-related adverse events reported annually increased in the post-ACIP guideline period, probably due at least in part to the increase in the number of infants receiving the vaccine, the authors note.

Of note, the safety profile of the trivalent influenza vaccine in the pre- and post-ACIP guideline periods were similar.

The four most commonly reported adverse events were fever, rash, seizure, and injection site reaction.

Seizures made up a large proportion of serious and overall adverse event reports after trivalent influenza vaccination among those younger than 2, although the absolute number (28) was relatively small. Nineteen of the seizure reports (68 percent) described fever with the seizure.

Fever-related seizure may or may not be caused by the trivalent influenza vaccine, the authors emphasize. Fever-related seizures are common among children 6 months to 2 years of age, have been linked to some childhood vaccines, and have not been found to result in serious long-term effects.

McMahon’s team reminds readers that VAERS is a passive surveillance system and the relative frequency of adverse events reporting may or may not reflect the actual incidence of these events - which can only be garnered with active surveillance or a clinical trial.

SOURCE: Pediatrics, February 2005.