A dose-ranging study of a subunit Respiratory Syncytial Virus subtype A vaccine with and without aluminum phosphate adjuvantation in adults ≥65 years of age

We studied the safety and immunogenicity of a Respiratory Syncytial Virus (RSV)-A vaccine containing subunit antigens F, G and M in older persons, and its effect on influenza vaccine immunogenicity. In a dose-ranging, placebo-controlled, blinded trial 561 adults ≥65 years of age at five Canadian sites were randomized to one intramuscular injection of either 100, 50 or 25 μg RSV-A-alum vaccine or 100 μg non-adjuvanted RSV-A vaccine, or alum-placebo. All participants were offered inactivated influenza vaccine on day 32. Immunization was well tolerated and reactogenicity was similar between the RSV and influenza vaccines and the alum-placebo. Only the 100 μg non-adjuvanted RSV vaccine achieved the primary immunogenicity outcome of eliciting a ≥4-fold rise in neutralizing antibody (NA) titres against RSV-A in ≥50% of participants at day 32. Geometric mean titres against RSV-A and -B at all points were comparable in 100 μg adjuvanted and non-adjuvanted groups. At day 32, a ≥4-fold haemagluttinin inhibition (HI) antibody response or HI ≥40 to Influenza (A-H3N2) was seen in >74% of participants; no difference was seen between groups. A subunit non-alum-containing RSV-A vaccine was well tolerated in a large population ≥65 years and did not interfere with influenza vaccine immunogenicity. This RSV-A-based vaccine demonstrated NA rise which could provide seasonal protection against severe RSV illnesses from RSV-A or -B and warrants further testing to determine its efficacy in the prevention of clinical illness in elderly persons.