Immunogenicity and safety of a 2009 pandemic influenza A (H1N1) monovalent vaccine in Chinese infants aged 6-35 months: a randomized, double-blind, controlled phase I clinical trial.

Objectives: The goal of this double-blind, randomized, controlled clinical trial was to assess the safety and immunogenicity of two different doses of a monovalent split-virion 2009 pandemic influenza A/H1N1 vaccine without adjuvant in Chinese infants aged 6-35 months. DESIGN AND SETTING  Subjects were randomly assigned to receive either a 2009 pandemic (H1N1) vaccine containing 7.5 or 15 μg haemagglutinin (HA) or a seasonal influenza vaccine. 2 doses of the H1N1 vaccines or the seasonal influenza vaccine were given 21 days apart in younger infants aged 6-23 months or older infants aged 24-35 months.

Sample: Serum samples were collected immediately before the first injection and before and 21 days after the second injection.

Main Outcome Measures: Primary outcomes were haemagglutinin inhibition (HI) antibody responses 21 days following each vaccination. Safety was monitoring throughout the study.

Results: The first vaccination of 7.5 μg and 15 μg H1N1 vaccine induced seroprotective antibody titers (HI titers≥1: 40) in 42.9-57.4% of younger infants and 49.1-61.0% older infants. Immune responses after completion of the two dose schedule were comparable in both age groups with seroprotective rates of 91-98% in each vaccine and age group and GMTs of 173-263. The H1N1 vaccine elicited similar rates of local and systemic adverse reactions as the seasonal influenza vaccine.

Conclusions: The 2009 pandemic influenza A /H1N1 vaccine were highly immunogenic in infants aged 6-35 months, and displayed a safety and reactogenicity profile similar to the seasonal influenza vaccine.

Trial Registration: ClinicalTrial.gov identifier: NCT01047202.