Safety and Immunogenicity of a Vero Cell Culture-Derived Whole-Virus Influenza A(H5N1) Vaccine in a Pediatric Population

Background. Children are highly vulnerable to infection with novel influenza viruses. It is essential to develop candidate pandemic influenza vaccines that are safe and effective in the pediatric population. Methods. Infants and children aged 6-35 months and 3-8 years, respectively, were randomized to receive 2 immunizations with a 7.5-mu g or 3.75-mu g hemagglutinin (HA) dose of a nonadjuvanted whole-virus A/Vietnam(H5N1) vaccine; adolescents aged 9-17 years received a 7.5-mu g dose only. A subset of participants received a booster immunization with an A/Indonesia(H5N1) vaccine approximately 1 year later. HA and neuraminidase antibody responses were assessed. Results. Vaccination was safe and well tolerated; adverse reactions were transient and predominantly mild. Two immunizations with the 7.5-mu g dose of A/Vietnam vaccine induced virus microneutralization (MN) titers of >= 1:20 against the A/Vietnam strain in 68.8%-85.4% of participants in the different age groups. After the booster, 93.1%-100% of participants achieved MN titers of >= 1:20 against the A/Vietnam and A/Indonesia strains. Neuraminidase-inhibiting antibodies were induced in >= 90% of participants after 2 immunizations with the 7.5 mu g A/Vietnam vaccine and in 100% of participants after the booster. Conclusions. A whole-virus influenza A(H5N1) vaccine is suitable for prepandemic or pandemic immunization in a pediatric population.