Safety of Trivalent Inactivated Influenza Vaccine in Children 24 to 59 Months Old

Background:
In 2006, recommendations for trivalent inactivated influenza (TIV) vaccination were expanded to include all children 24 to 59 months old. To date, information on the safety of TIV in this age group is limited, and no studies have examined the risk of medically attended events (MAEs) in children who received multiple annual doses in childhood.

Objectives:
To examine the risk of MAEs following TIV in children ages 24 to 59 months and to analyze whether having received multiple annual TIV doses is associated with increased risk for MAEs.

Methods:
We studied a retrospective cohort of 66,737 children who received 92,905 vaccinations between October 1, 2002 and March 31, 2006. The data source included electronic administrative data from seven managed care organizations that participate in the Vaccine Safety Datalink (VSD). Within the cohort, we examined the risk of pre-specified MAEs using a self-controlled case series analysis, with risk windows of 0-2 days, 1-3 days, 1-14 days, or 1-42 days following TIV.

Results:
Preliminary analyses of administrative diagnoses codes suggest limb soreness and swelling were more likely to occur 0-2 days after vaccination (adjusted incidence rate ratio [IRR] 3.20, 95% confidence interval [CI] 1.19 – 8.59), as was cellulitis and skin infection (IRR 3.52, CI 1.00 – 12.45). Fever was more likely to occur 1-14 days after TIV (IRR 1.40, CI 1.09 – 1.80) as was gastrointestinal illness (IRR 1.52, CI 1.18 – 1.95). Allergic and vaccine reactions were more likely to occur 1-3 days and 1-14 days after vaccination, and the risk of having such a reaction increased with each dose of influenza vaccine across seasons.

Conclusions:
Preliminary analyses of administrative data suggest small or moderate increased risk of several MAEs after TIV. Administrative diagnoses codes may not be associated with the vaccination or may be miscoded; therefore, medical record review is underway to confirm these findings.