• Chinese infant;
  • H1N1;
  • pandemic influenza vaccine;
  • seasonal influenza vaccine

Please cite this paper as: Li et al. (2012) 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. Influenza and Other Respiratory Viruses DOI: 10.1111/irv.12028.

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 identifier: NCT01047202