Adverse events after inactivated influenza vaccination among children less than 2 years of age: Analysis of reports from the Vaccine Adverse Event Reporting System, 1990-2003

Background. In April 2002, the Advisory Committee on Immunization Practices ( ACIP) encouraged providers to vaccinate healthy 6- to 23-month-old infants and children with trivalent influenza vaccine (TIV). Objectives. To describe adverse events (AEs) reported to the Vaccine Adverse Event Reporting System (VAERS) after TIV vaccination among children <2 years of age and to compare reports before the ACIP guideline (January 1990 to June 2002) and after the ACIP guideline (July 2002 to June 2003). Methods. VAERS is a passive vaccine safety surveillance system begun by the Food and Drug Administration and the Centers for Disease Control and Prevention in 1990. We reviewed reports to VAERS for children <2 years of age who received TIV, alone or in combination with other vaccines. Influenza seasons were defined as the period from July 1 of one year to June 30 of the following year. Results. Between 1990 and 2003, VAERS received 166 TIV reports for children <2 years of age. There were 62 reports (37%) after administration of TIV alone and 104 reports (63%) after administration of TIV and >= 1 other vaccine. Approximately one third of reports (N=61) were in the post-ACIP guideline period. The 4 most frequent AE coding terms were fever (N=59, 35%), unspecified or urticarial rash ( 42, 25%), seizure (28, 17%), and injection site reaction (28, 17%). The median number of days from vaccination to symptom onset, the percentage of reports that represented serious AEs, and the gender distribution were similar in the pre-ACIP guideline and post-ACIP guideline periods. The percentage of reports describing an underlying medical condition for the subject decreased from 58% before the ACIP guideline to 37% after the ACIP guideline. Nineteen of 28 seizure reports (68%) described fever with the seizure within 2 days after vaccination. Seizure was the most frequent coding term (N=10, 7 with fever) among 23 serious reports. The annual number of TIV-related VAERS reports for children <2 years of age increased in the post-ACIP guideline period, probably at least in part because of an increase in the number of vaccinees after the ACIP announcement. The safety profiles in the pre-ACIP guideline and post-ACIP guideline periods were similar. Conclusions. In October 2003, the ACIP recommended that all healthy children 6 to 23 months of age be vaccinated with TIV, starting in the 2004-2005 influenza season. This study provides generally reassuring, although limited, data regarding the safety of TIV among children in this age range. Continued surveillance for seizures and other clinically significant AEs is warranted and will continue.