Effectiveness of Pfizer’s RSV vaccine could reduce disease burden in older adults

Key takeaways:

• RSVpreF showed effectiveness of 90% or higher regardless of the study controls used.
• The results fill data gaps among groups called out in the ACIP’s 2024 update to RSV vaccine guidelines.

The bivalent respiratory syncytial virus prefusion F, or RSVpreF, vaccine may prevent one hospitalization or ED visit tied to the infection for every 250 vaccinated older adults, an analysis showed.

The data are consistent with recent findings on respiratory syncytial virus (RSV) vaccine effectiveness and suggest the opportunity “to reduce severe medically attended RSV disease burden,” the researchers wrote in JAMA Network Open.

The CDC’s Advisory Committee on Immunization Practices (ACIP) said in June 2023 that adults 60 years of age or older may receive one of the two RSV vaccines approved by the FDA after talking with their doctors about being vaccinated.

Sara Y. Tartof, PhD, MPH, an infectious disease epidemiologist at Kaiser Permanente Department of Research and Evaluation, and colleagues noted that the ACIP cited a lack of evidence from phase 3 pivotal trials on vaccine effectiveness against RSV-related hospitalizations and ED visits in those at high risk.

The researchers assessed the protective effects of Pfizer’s RSVpreF, also known as Abrysvo, against such outcomes among adults aged 60 years or older in a large U.S. health care network.

Tartof and colleagues used two sets of controls:

• strict controls, which included lower respiratory tract disease (LRTD)-related events that were negative for RSV, SARS-CoV-2, influenza and human metapneumovirus and positive for a cause not preventable by a vaccine; and
• broad controls, which included all RSV-negative LRTD events.

The retrospective case-control study included 7,047 hospitalizations or ED visits that occurred between Nov. 24, 2023, and April 9, 2024. Cases had an established relation to LRTD and RSV testing results.

The study group had a mean age of 78 years and included 54.2% women and 36.9% non-Hispanic white individuals. Additionally, 14.2% were immunocompromised and 93.3% had one or more Charlson comorbidity.

The researchers found an estimated adjusted vaccine effectiveness of 91% (95% CI, 59%-98%) when strict controls were used, with those vaccinated having received RSVpreF a median 61 days before their LRTD encounter.

The reported vaccine effectiveness of 90% (95% CI, 59%-97%) using broad controls, with vaccinated adults having received RSVpreF a median 58 days before the LRTD encounter.

Tartof and colleagues underlined that the results are particularly significant “as they address data gaps for groups called out” in the ACIP’s 2024 update to their guidance on the use of RSV vaccines.

Specifically, that guidance recommends vaccination for all adults aged 75 years or older and for adults aged 60 to 74 years at an increased risk for severe RSV.

The researchers also acknowledged several study limitations. For example, the vaccination rate was lower than what national estimates report, while the analysis’ vaccine effectiveness estimates may be biased to the null or contrariwise “if our vaccinated population is older and with more comorbidities than recipients nationwide.”

“Further case accrual and vaccine uptake after the 2024 to 2025 RSV season will continue and will power future stratified analyses,” they wrote. “Multiseason future analyses will be better suited to capture potential waning of protection with time since vaccination.”