An adjuvanted, postfusion F protein-based vaccine did not prevent respiratory syncytial virus illness in older adults

Abstract

Background. Respiratory syncytial virus (RSV) is an important cause of illness in older adults. This study assessed efcacy of a vaccine for prevention of RSV-associated acute respiratory illness (ARI), defned by specifed symptoms with virologic confrmation. Methods. This phase 2b study evaluated RSV postfusion F protein (120 μ g) with glucopyranosyl lipid adjuvant (5 μ g) in 2% stable emulsion. Subjects aged =60 years were randomly assigned at a ratio of 1:1 to receive vaccine or placebo (all received inactivated influenza vaccine). Ill subjects recorded symptoms and provided blood and nasal swab samples. Results. In the per-protocol population (n = 1894), the incidence of RSV-associated ARI occurring =14 days afer dosing was 1.7% and 1.6% in the vaccine and placebo groups, respectively, for a vaccine efcacy (VE) of-7.1% (90% confdence interval [CI],-106.9%-44.3%). Efcacy was not observed in secondary analyses that included seroresponse to nonvaccine RSV antigens (VE, 8.9%; 90% CI,-28.5%-35.4%) or symptoms combined with seroresponse (VE, 10.0%; 90% CI,-45.4%-44.4%). On day 29, 92.9% of vaccinees had an anti-F immunoglobulin G antibody seroresponse. Overall, 48.5% and 30.9% of RSV vaccine recipients reported local and systemic solicited symptoms, respectively. Conclusion. Te RSV vaccine was immunogenic but did not protect older adults from RSV illness.