Serum immunoglobulin levels do not affect antibody responses to influenza HA vaccine in preterm infants

Antibody responses to two doses of influenza hemagglutinin (HA) vaccine were evaluated in 45 previously unimmunized preterm infants aged 6–11 months before the 2003/2004 influenza season. Twenty-three (51.1%), 21 (46.6%) and 2 (4.4%) of the subjects acquired protective (≥1:40) hemagglutination inhibition (HI) antibody titers after vaccination for A/New Caledonia (H1N1), A/Panama (H3N2) and B/Shandong, respectively. Antibody responses to A (H1N1), A (H3N2) appeared to be comparable to those reported on full-term infants of similar ages vaccinated with the identical vaccine. Serum IgG levels at vaccination had no positive association with antibody responses on univariate or multivariate analysis, indicating that prolonged hypogammaglobulinemia after 6 months of age in preterm infants was not a factor to affect antibody responses to influenza HA vaccine.