Transplacental transfer of maternal respiratory syncytial virus (RSV) antibody and protection against RSV disease in infants in rural Nepal

Background Respiratory syncytial virus (RSV) is the most important viral cause of pneumonia in children. RSV-specific antibody (ab) protects infants from disease, and may be increased by a potential strategy of maternal RSV vaccination. Objectives To describe the effect of RSV antibody on RSV infection risk in infants in a resource-limited setting. Study design In a prospective study in Nepal, women were enrolled during pregnancy and maternal and infant cord blood were collected at birth. Weekly surveillance for respiratory illness was performed from birth to 180 days. Nasal swabs were tested for RSV by PCR and serum was tested using an RSV antibody microneutralization assay. Antibody concentrations at time of RSV infection were estimated based on a decay rate of 0.026 log₂/day. Results Cord:maternal RSV antibody transfer ratio was 1.03 (0.88–1.19), with RSV antibody concentration of log₂ 11.3 and log₂ 11.7 in 310 paired maternal and infant samples, respectively. Cord blood RSV antibody was log₂ 12.1 versus 11.6 in those with or without RSV infection (P = 0.86). Among infants with RSV infection, estimated RSV antibody concentration at time of infection did not differ in infants with upper (n = 8; log₂ 10.7) versus lower respiratory tract infection (n = 21; log₂ 9.8; P = 0.37). Cord blood RSV antibody concentrations did not correlate with age at primary RSV infection (R = 0.11; P = 0.57). Conclusions Transplacental transfer of RSV antibody from mother to the fetus was highly efficient in mother-infant pairs in rural Nepal, though higher antibody concentrations were not protective against earlier or more severe RSV infection in infants.