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Respiratory syncytial virus prefusion F candidate vaccine is safe and can boost humoral and cell-mediated immune responses in older adults.

Respiratory syncytial virus (RSV) causes respiratory tract infections with seasonal peaks. Natural immunity is incomplete and short-lived. Severe RSV-associated lower respiratory tract disease (RSV-LRTD) occurs in older adults (mostly ≥60 years), especially with underlying medical conditions. There is no available vaccine or prophylaxis against RSV-LRTD in older adults. 

A study in The Journal of Infectious Diseases has evaluated the safety and immunogenicity of RSV candidate vaccine formulations containing the stabilized prefusion conformation of RSV fusion protein (RSVPreF3) in older adults.

Study Design and Population

This phase 1/2 randomized clinical trial comprised 1005 older adults who received at least one dose of vaccine or placebo, and 970 who received two doses. The mean age was 67.6 years, and 57% of the participants were female. RSVPreF3 formulations included 30, 60, and 120 μg antigen concentrations and were unadjuvanted (Plain), or adjuvanted with AS01E or AS01B.

Favorable Safety Findings in Vaccine Trial

No safety concerns precluding the use of any vaccine formulation were identified throughout the trial. Solicited adverse events (AEs) were more frequent in AS01 (highest for AS01B) than in unadjuvanted and placebo groups. Within 7 days of vaccination, 43.3–52.0% of plain, 71.3–79.0% of AS01E, 86.4–88.0% of AS01B, and 37.0% of placebo recipients reported at least one solicited AE. Grade 3 solicited administration-site events were reported with plain (0–2%), AS01E (2–3%), and AS01B (5–8.7%) RSVPreF3 formulations, but not with placebo. Grade 3 systemic solicited AEs were reported by 1% of placebo and 3% of 120-Plain, 3% of 30-AS01E, and 4% of 60-AS01B RSVPreF3 vaccine recipients. The reported solicited AEs were mostly mild and transient.

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Similar proportions of placebo and 60-AS01E and 120-AS01B RSVPreF3 vaccine recipients reported unsolicited AEs within 30 days post-vaccination. Of these, only one grade 3 AE was vaccine-related.

RSVPreF3 Vaccination Enhances Immune Responses

Participants showed detectable baseline RSV-specific antibodies due to previous exposure. Baseline RSVPreF3-specific CD4+ T-cells were below the lower limit. RSVPreF3 vaccination significantly increased antibody levels and CD4+ T-cell frequencies compared to pre-vaccination. Adjuvants significantly increased cell-mediated immune responses compared to plain, with a statistically significant effect of AS01B over AS01E.

Strong Immune Responses Elicited by RSVPreF3 Vaccine Formulations

All vaccine formulations invoked a significantly higher RSV-A neutralizing antibody response than placebo. A statistically significant positive linear effect of RSVPreF3 antigen concentration with all vaccine groups was demonstrated regarding RSV-A nAb geometric mean titers. The RSVPre3F vaccine also induced robust RSV-B nAb, RSVPre3F-specific IgG, and RSVPreF3-epitope-specific antibody (RSB1) responses.

Considering the benefits of the formulations with the highest RSVPreF3 antigen level (120 μg) and less reactogenicity, the 120-AS01E formulation has been selected for further clinical evaluation.


Leroux-Roels, I., Davis, M. M., Steenackers, K., Essink, B., Vandermeulen, C., Fogarty, C., Andrews, C. M., Kerwin, E., David, M., Fissette, L., Vanden Abeele, C., Collete, D., De Heusch, M., Salaun, B., De Schrevel, N., Koch, J., Verheust, C., Dezutter, N. A., Struyf, F., . . . Hulstrøm, V. (2022). Safety and Immunogenicity of a Respiratory Syncytial Virus Prefusion F (RSVPreF3) Candidate Vaccine in Older Adults: Phase 1/2 Randomized Clinical Trial. The Journal of Infectious Diseases, 227(6), 761–772. https://doi.org/10.1093/infdis/jiac327