Safety and Immunogenicity Following Administration of a Live, Attenuated Monovalent 2009 H1N1 Influenza Vaccine to Children and Adults in Two Randomized Controlled Trials

BACKGROUND: The safety, tolerability, and immunogenicity of a monovalent intranasal 2009 A/H1N1 live attenuated influenza vaccine (LAIV) were evaluated in children and adults. METHODS/PRINCIPAL FINDINGS: Two randomized, double-blind, placebo-controlled studies were completed in children (2–17 y) and adults (18–49 y). Subjects were assigned 4∶1 to receive 2 doses of H1N1 LAIV or placebo 28 days apart. The primary safety endpoint was fever ≥38.3°C during days 1–8 after the first dose; the primary immunogenicity endpoint was the proportion of subjects experiencing a postdose seroresponse. Solicited symptoms and adverse events were recorded for 14 days after each dose and safety data were collected for 180 days post-final dose. In total, 326 children (H1N1 LAIV, n = 261; placebo, n = 65) and 300 adults (H1N1 LAIV, n = 240; placebo, n = 60) were enrolled. After dose 1, fever ≥38.3°C occurred in 4 (1.5%) pediatric vaccine recipients and 1 (1.5%) placebo recipient (rate difference, 0%; 95% CI: –6.4%, 3.1%). No adults experienced fever following dose 1. Seroresponse rates in children (H1N1 LAIV vs. placebo) were 11.1% vs. 6.3% after dose 1 (rate difference, 4.8%; 95% CI: –9.6%, 13.8%) and 32.0% vs. 14.5% after dose 2 (rate difference, 17.5%; 95% CI: 5.5%, 27.1%). Seroresponse rates in adults were 6.1% vs. 0% (rate difference, 6.1%; 95% CI: –5.6%, 12.6%) and 14.9% vs. 5.6% (rate difference, 9.3%; 95% CI: –0.8%, 16.3%) after dose 1 and dose 2, respectively. Solicited symptoms after dose 1 (H1N1 LAIV vs. placebo) occurred in 37.5% vs. 32.3% of children and 41.7% vs. 31.7% of adults. Solicited symptoms occurred less frequently after dose 2 in adults and children. No vaccine-related serious adverse events occurred. CONCLUSIONS/SIGNIFICANCE: In subjects aged 2 to 49 years, two doses of H1N1 LAIV have a safety and immunogenicity profile similar to other previously studied and efficacious formulations of seasonal trivalent LAIV. TRIAL REGISTRATION: ClinicalTrials.gov NCT00946101, NCT00945893