RSV vaccine prompts robust immune response in older recipients over 2 seasons

The respiratory syncytial virus (RSV) vaccine triggered strong immune responses among people aged 60 years and older during its first two seasons for use, according to the final findings of a phase 3 randomized controlled trial published last week in Clinical Infectious Diseases.

For the RENOIR (RSV Vaccine Efficacy Study in Older Adults Immunized against RSV Disease) study, a research team led by 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 Pfizer’s bivalent (two-strain) RSV Prefusion F (RSVpreF) vaccine or a placebo. The respiratory syncytial virus (RSV) vaccine triggered strong immune responses among people aged 60 years and older during its first two seasons for use,

The immunogenicity subset was made up of 1,151 participants, and the evaluable immunogenicity population included 1,067. The investigators collected blood samples from participants before and 1 month after vaccination and before the second RSV season from August 2021 to December 2023.

The median participant age was 67 years, 62.6% were aged 60 to 69 years, 5.5% were aged 80 and older, 51% were men, 80% were White, 12% were Black, 41% were Hispanic, and 52.3% had at least one high-risk chronic condition.

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.

Favorable safety profile

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. 

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.

In the RSVpreF group, proportions of participants with immune responses were higher 1-month postvaccination (RSV-A, 84.3%; RSV-B, 85.6%) than at the preseason-2 visit (59.4% and 57.5%, respectively) and much higher than placebo (less than 3.0% and less than 7.7%, 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% of RSVpreF and 6.1% of those in the placebo group reporting a serious adverse event.

The previously reported vaccine efficacy (VE) was 88.9% and 77.8% effective against infection with at least three symptoms among people aged 60 years and older during its first two seasons of use, respectively. That previous study noted that VE against medically attended RSV with at least three symptoms, medically attended infection with two or more symptoms, and medically attended RSV infection was 76.3%, 60.0%, and 53.2%, respectively.

“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,” the study authors concluded.