Safety of the trivalent inactivated influenza vaccine among children: a population-based study

Abstract

Background: To our knowledge, there are no published population-based studies on the safety of the inactivated trivalent influenza vaccine among children.

Objective: To screen a large population of children for evidence of increased medical visits in the 2 weeks after influenza vaccination compared with 2 control periods. Secondary analyses included shorter risk periods and restricted age categories.

Design: Self-control screening analysis. Children vaccinated from January 1, 1993, through December 31, 1999, were randomly divided into 2 equal groups. In group 1, risks of outpatient, emergency department, and inpatient visits during the 14 days after vaccination were compared with the risks of visits in 2 control periods. Significant plausible medically attended events identified in group 1 were then analyzed in group 2, using the same 2 control periods. Medically attended events significant in both groups were considered potentially associated with vaccination and were assessed by medical record review.

Setting: Five managed care organizations in the United States.

Participants: Children younger than 18 years who received an influenza vaccination in one of the managed care settings (N = 251 600).

Main outcome measure: Among vaccinated children seen for a medically attended event, the odds of the visit occurring in the 2 weeks after vaccination vs during 1 of the 2 control periods.

Results: Study participants incurred 1165, 230, and 489 different diagnoses during the 14 days after vaccination according to the outpatient, emergency department, and inpatient data, respectively. Four diagnoses were positively associated with the vaccine in both groups 1 and 2: impetigo, dermatitis, uncomplicated diabetes mellitus, and ureteral disorder not otherwise specified. After medical record review, impetigo (9 cases) in children 6 to 23 months old remained significantly associated with vaccination.

Conclusion: This large screening safety study did not reveal any evidence of important medically attended events associated with pediatric influenza vaccination.