Level of Maternal Respiratory Syncytial Virus (RSV) F Antibodies in Hospitalized Children and Correlates of Protection.

RSV is a major cause of lower respiratory infections among children, where no vaccine is available. The stabilized form of the fusion (F) protein, pre-F, is a leading vaccine candidate targeting 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. 65 paired blood samples were collected from RSV-infected children below six months of age, and their corresponding mothers. All pairs were screened for pre-F and post-F antibodies levels using ELISA. The neutralizing antibodies (NAbs) in both groups were measured in-vitro against mKate RSV-A2 using H28 cells. Only 14% of matAbs (log 12.8) were present in infants at hospitalization, with an average log EP titer of 10.2 directed to both F-protein conformations. Additionally, 61.4% of maternal NAbs (log EC = 9.4) were detected in infants (log EC = 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 infants' 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