Efficacy and safety of 1 and 2 doses of live attenuated influenza vaccine in vaccine-naive children.

Federal University of São Paulo, São Paulo, Brazil.
The Pediatric Infectious Disease Journal (Impact Factor: 2.72). 05/2009; 28(5):365-71.
Source: PubMed


We investigated the efficacy and safety of 1 versus 2 doses of live attenuated influenza vaccine (LAIV) in influenza vaccine-naive children aged 6 to <36 months.
Subjects were randomized to 1 of 4 regimens in year 1: 2 doses LAIV, 1 dose LAIV, excipient placebo, or saline placebo. In year 2, LAIV recipients were to receive 1 dose of LAIV and placebo recipients were to receive saline placebo. Because of an unintended treatment allocation error in year 2, 1 block of subjects who were randomized to LAIV received saline placebo and 1 block who were randomized to placebo received LAIV.
In year 1, vaccine efficacy versus placebo among recipients of 2 and 1 doses of LAIV was 73.5% and 57.7%, respectively, against antigenically similar strains. In year 2, absolute efficacy of a single dose of LAIV was 73.6% and 65.2%, respectively, in recipients of 2 and 1 doses of LAIV in year 1. Year 2 efficacy was 57.0% in subjects who received 2 doses of LAIV in year 1 and placebo in year 2. Safety and tolerability of LAIV were consistent with previous studies. Reactogenicity was similar between placebo groups. Seroconversion rates were significantly higher in the 2-dose versus the 1-dose LAIV group in year 1 and in both LAIV groups versus placebo in years 1 and 2.
One dose of LAIV provided clinically significant protection against influenza in young children previously unvaccinated against influenza; 2 doses provided additional protection. Protection after 2 doses in year 1 persisted through a second season without revaccination. LAIV excipients were not a major contributor to reactogenicity. These benefits provide support for increased use of LAIV in children > or =2 years of age.

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    • "The vaccine is administered as a nasal spray using the Accuspray device (Becton Dickinson, Franklin Lakes, NJ, USA). Nine randomized, controlled clinical trials have evaluated the efficacy of LAIV against culture-confirmed influenza illness compared with placebo or trivalent inactivated influenza vaccine (TIV) [9] [10] [11] [12] [13] [14] [15] [16] [17] [18]. A previous meta-analysis of these trials by Rhorer et al. [19] evaluated the efficacy of LAIV in children in all subjects enrolled, many of whom were 6–23 months of age. "
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