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

Background: 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. Methods: 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-A(2) using H28 cells. Results: 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) EC50 = 9.4) were detected in infants (log(2) EC50 = 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. Conclusions: 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. (C) 2021 The Authors. Published by Elsevier Ltd on behalf of International Society for Infectious Diseases.