RSV Vaccine Prompts Robust Response in Older Recipients

Findings of a Phase III randomized controlled trial showed Pfizer’s RSV Prefusion F (RSVpreF) vaccine triggered strong immune responses among people aged 60 years and older during its first two seasons.

The RENOIR (RSV vaccine efficacy study in older adults immunized against RSV disease) study led by a research team at the University of Rochester and RSV vaccine manufacturer Pfizer randomly assigned a subset of participants in the United States and Japan in a 1:1 ratio to receive one dose of the vaccine or a placebo. The vaccine, sold under the brand name Abrysvo, contains molecules called antigens designed to produce an immune response against RSV-A and RSV-B. It is approved for preventing RSV infection in adults aged 60 years and older, those aged 18 to 59 at increased risk for severe illness and infants through maternal vaccination.

The immunogenicity subset was made up of 1,151 participants, and the evaluable immunogenicity population included 1,067. The median participant age was 67 years, 62.6 percent of whom were aged 60 to 69 years, 5.5 percent of whom were aged 80 and older, 51 percent of whom were men, 80 percent of whom were White, 12 percent of whom were Black, 41 percent of whom were Hispanic and 52.3 percent of whom had at least one high-risk chronic condition. 

The investigators collected blood samples from participants before and one month after vaccination and before the second RSV season from August 2021 to December 2023. One month after vaccination, the geometric mean fold rise (GMFR) in levels of neutralizing antigens was 12.1 for RSV-A and -B. Geometric mean titers declined at the second preseason visit but stayed substantially higher than baseline (4.7). One month postvaccination, GMFRs for neutralizing responses were 12.0 to 13.0 for subgroups stratified by age-group. 

In the RSVpreF group, proportions of participants with immune responses were higher one month postvaccination (RSV-A, 84.3 percent; RSV-B, 85.6 percent) than at the preseason-2 visit (59.4 percent and 57.5 percent, respectively) and much higher than placebo (less than 3.0 percent and less than 7.7 percent, respectively, at any timepoint). RSV-A and -B GMFRs in participants with selected chronic conditions were generally comparable to those of their otherwise healthy peers (range, 11.4 to 14.4). The vaccine also showed a favorable safety profile during both seasons, with 6.2 percent of RSVpreF and 6.1 percent of those in the placebo group reporting a serious adverse event.

These data from the RENOIR study continue to support vaccination of older adults with bivalent RSVpreF to prevent RSV illness from both RSV-A and RSV-B subgroups.