Protective efficacy against respiratory syncytial virus following murine neonatal immunization with BBG2Na vaccine: Influence of adjuvants and maternal antibodies

Alum-adsorbed BBG2Na, a recombinant vaccine derived in part from the respir atory syncytial virus (RSV) subgroup A G protein, induced moderate antibody titers after 1 immunization in I-week-old mice but conferred complete lung protection upon RSV challenge. The anti-BBG2Na IgG1-IgG2a neonatal isotype profile was suggestive of dominant Th2 responses compared with those in ad ults. Formulation of BBG2Na with a Th1-driving adjuvant efficiently shifted neonatal responses toward a more balanced and adultlike IgG1-IgC2a profile without compromising its protective efficacy, BBG2Na-induced protective im munity was maintained even after early life immunization in the presence of high titers of maternal antibodies, Under these conditions, the protective efficacy (86%-100%) reflected the high capacity of the nonglycosylated G2N a immunogen to escape inhibition by RSV-A-induced maternal antibodies. Thus , immunization with BBG2Na protected against viral challenge despite neonat al immunologic immaturity and the presence of maternal antibodies, two majo r obstacles to neonatal RSV vaccine development.