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Pediatr Infect Dis J. 2009 May;28(5):365-71. doi: 10.1097/INF.0b013e31819219b8.

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

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  • 1Federal University of São Paulo, São Paulo, Brazil.

Abstract

BACKGROUND:

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.

PATIENTS/METHODS:

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.

RESULTS:

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.

CONCLUSIONS:

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.

PMID:
19395948
[PubMed - indexed for MEDLINE]
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