Virus-Specific Antibody, Viral Load, and Disease Severity in Respiratory Syncytial Virus Infection

Background. Maternally derived serum antibody and viral load are thought to influence disease severity in primary respiratory syncytial virus (RSV) infection. As part of the AsPIRES study of RSV pathogenesis, we correlated various serum antibody concentrations and viral load with disease severity. Methods. Serum neutralizing antibody titers and levels of immunoglobulin G (IgG) to RSV fusion protein (F), attachment proteins of RSV group A and B, the CX3C region of G, and nasal viral load were measured in 139 full-term previously healthy infants with primary RSV infection and correlated with illness severity. Results. Univariate analysis showed no relationship between measures of serum antibody and severity. However, a multivariate model adjusting for age at the time of infection found a significant 0.56 decrease in severity score for each 2-fold increase in antibody concentration to RSV F. The benefit of antibody was greatest in infants <= 2 months of age. Additionally, estimated antibody titer at birth was correlated with age at infection, suggesting that higher antibody titers delay infection. Viral load did not differ by illness severity. Conclusion. Our data support the concept of maternal immunization with an RSV vaccine during pregnancy as a strategy for reducing the burden of RSV infection in full-term healthy infants exposed to RSV during their first winter.