Profiling the dynamics of maternally acquired and infection-induced antibodies against influenza B in early childhood: a longitudinal paired mother-infant cohort study from southern China.

BackgroundInfluenza B virus infection can cause clinical outcomes that are as severe as those caused by influenza A in young children. However, the early-life immunological trajectory of influenza B remains poorly characterised. We aimed to assess the transplacental transfer and decay of maternal antibodies, and characterise the dynamics and cross-reactivity of infection-induced antibodies in early childhood.MethodsBetween Sept 20, 2013, and Oct 14, 2015, we enrolled 1054 mothers and their 1066 infants in a prospective cohort study in China. Eligible participants were mothers who delivered at the study sites and provided written informed consent for themselves and their infants. Among these individuals, 531 mothers and their 534 neonates were selected for the present analysis via stratified random sampling. Maternal venous and cord blood were collected at delivery, with follow-up serum samples from children at 2, 4, 6, 12, 24, and 36 months and at 5-8 years. Haemagglutination inhibition assays measured titres against four B/Victoria and two B/Yamagata strains. We assessed the transplacental transfer efficiency and the half-life as well as the time-to-loss of maternal antibodies and characterised the kinetics and cross-reactivity of influenza B infection-induced antibodies from birth to 5-8 years.FindingsMaternal antibodies were efficiently transferred (mean transfer ratio 0·9-1·0), and neonatal antibody titres were strongly correlated with maternal titres (r>0·8, p