Safety and Immunogenicity of a Respiratory Syncytial Virus Fusion (F) Protein Nanoparticle Vaccine in Healthy Third-Trimester Pregnant Women and Their Infants

Background: Respiratory syncytial virus (RSV) is the leading cause of infant lower respiratory tract disease and hospitalization worldwide.

Methods: Safety and immunogenicity of RSV fusion (F) protein nanoparticle vaccine or placebo were evaluated in 50 healthy third-trimester pregnant women. Assessments included vaccine tolerability and safety in women and infants, and RSV-specific antibody measures in women before and after vaccination, at delivery and post partum.

Results: The vaccine was well tolerated; no meaningful differences in pregnancy or infant outcomes were observed between study groups. RSV-specific antibody levels increased significantly among vaccine recipients, including responses competitive with well-described monoclonal antibodies specific for multiple RSV neutralizing epitopes. No significant antibody increase was seen among placebo recipients, although a shallow upward trend across the RSV season was noted. Transplacental antibody transfer was 90%-120% across assays for infants of vaccinated women. Women with an interval of ≥30 days between vaccination and delivery demonstrated higher placental antibody transfer rates than women with an interval <30 days. Half-lives of RSV-specific antibodies in infants approximated 40 days. There was no evidence of severe RSV disease in infants of vaccinated mothers.

Conclusions: Data from this phase 2 study support a maternal immunization strategy to protect infants from RSV disease.

Clinical Trials Registration: NCT02247726.