A Respiratory Syncytial Virus Vaccine Based on the Small Hydrophobic Protein Ectodomain Presented With a Novel Lipid-Based Formulation Is Highly Immunogenic and Safe in Adults: A First-in-Humans Study

BACKGROUND: Respiratory syncytial virus infection can cause lower respiratory tract infection in older adults comparable to influenza, but no vaccines are available. METHODS: This was a randomized, observer-blinded, first-in-humans study of a novel synthetic RSV antigen based on the ectodomain of the small hydrophobic glycoprotein (SHe) of RSV subgroup A, formulated with either the lipid and oil–based vaccine platform DepoVax (DPX-RSV[A]) or alum (RSV[A]-Alum), in healthy, 50–64-year-old individuals. Two dose levels (10 or 25 µg) of SHe with each formulation were compared to placebo. A booster dose was administered on day 56. RESULTS: There was no indication that the vaccine was unsafe. Mild pain, drowsiness, and muscles aches were the most common solicited adverse events (AEs), and the frequencies of the AEs did not increase after dose 2. Robust anti-SHe–specific immune responses were demonstrated in the DPX-RSV(A) 10-μg and 25-μg groups (geometric mean titer, approximately 10-fold and 100-fold greater than that of placebo at days 56 and 236, respectively), and responses were sustained in the DPX-RSV(A) 25-μg group at day 421. Responses to the RSV(A)-Alum vaccines were very low. CONCLUSIONS: A novel antigen from the SH protein of RSV, formulated in a lipid and oil–based vaccine platform, was highly immunogenic, with sustained antigen-specific antibody responses, and had an acceptable safety profile.