Level of maternal respiratory syncytial virus (RSV) F antibodies in hospitalized children and correlates of protection.

• This study found that 14% of maternal antibodies were present in infants at hospitalization. • An average log 2 EP titer of 10.2 was directed to both F-protein conformations. • The neutralizing activity in infants was greater than that of binding antibodies. • One-third of infants had relatively high NAb titers, yet, they were hospitalized. Respiratory syncytial virus (RSV) is a major cause of lower respiratory infection among children and no vaccine is available. The stabilized form of the fusion (F) protein – pre-F – is a leading vaccine candidate to target different populations, including pregnant women. This study aimed to determine the magnitude and nature of RSV-directed maternal antibodies (matAbs) in hospitalized children with RSV infection. Sixty-five paired blood samples were collected from RSV-infected children aged <6 months and their corresponding mothers. All pairs were screened for levels of pre-F and post-F antibodies using ELISA. The neutralizing antibodies (NAbs) in both groups were measured in vitro against mKate RSV-A2 using H28 cells. It was found that 14% of matAbs (log 2 12.8) were present in infants at hospitalization, with an average log 2 EP titer of 10.2 directed to both F-protein conformations. Additionally, 61.4% of maternal NAbs (log 2 EC 50 = 9.4) were detected in infants (log 2 EC 50 = 8.7), which were mostly pre-F exclusive (81%). Pre-F antibodies in children showed a positive correlation with matAbs titers and negative correlations with age and bronchiolitis score. The maintenance of neutralizing activity in infants relative to maternal titers was greater than the maintenance of antibody binding based on ELISA, suggesting that higher-potency antibodies may have a longer half-life than weakly neutralizing antibodies. [ABSTRACT FROM AUTHOR]