Safety and effectiveness of the trivalent, cold-adapted influenza vaccine (CAIV-T) in children

Abstract

Background: We report on the safety and effectiveness of trivalent, cold-adapted influenza vaccine (CAIV-T) in children in the largest community trial to date. Methods: Enrolled children 18 months through 18 years of age received CAIV-T in years 1 (1998) and 2 (1999). All were surveyed for serious adverse events (SAEs). The relative risk (RR) of medically attended acute respiratory illness (MAARI) was estimated in the first 14 days after CAIV-T and compared to the reference interval pre-vaccine and >14 days after CAIV-T. Vaccine effectiveness against MAARI during the influenza outbreak was determined for vaccinees compared to age-eligible non-participants. Results: 4298 and 5250 children received CAIV-T in years 1 and 2. Twenty-two SAEs were identified; none were vaccine associated. No excess MAARI attributed to CAIV-T was observed: the RRs 0–14 days after CAIV-T were 1.0 (95% CI 0.8–1.3) and 1.1 (95% CI 0.8–1.4) for years 1 and 2, respectively. Similar safety was seen in a subgroup of children with mild wheezing illness. In year 1, vaccine effectiveness was detected during the intense period of the influenza season: RR 0.9 (95% CI: 0.81–0.99); year 2 is pending. Conclusions: CAIV-T was safe in children including those with mild wheezing illness. Effectiveness of CAIV-T was detected against MAARI.