Estimated Vaccine Effectiveness for Respiratory Syncytial Virus–Related Acute Respiratory Illness in Older Adults: Findings From the First Postlicensure Season

Abstract

Background Respiratory syncytial virus (RSV) is an important cause of severe respiratory illness among older adults. Previously, we showed that the RSVpreF vaccine (Abrysvo; Pfizer) prevents RSV-related lower respiratory tract disease–related emergency department (ED) visits/hospitalizations in older adults. Here, we evaluate its effectiveness against additional acute respiratory illness (ARI) end points, including severe disease, among high-risk persons. Methods This was a retrospective test-negative case-control study of adults aged ≥60 years at Kaiser Permanente Southern California with ARI ED visits/hospitalizations, defined by International Classification of Diseases, Tenth Revision discharge code, from 24 November 2023 to 9 April 2024. Case patients tested positive for RSV. Controls in the primary analysis tested negative for RSV, human metapneumovirus, influenza, and severe acute respiratory syndrome coronavirus 2 and positive for a non–vaccine-preventable pathogen. The exposure was RSVpreF receipt ≥21 days before ARI diagnosis. Vaccine effectiveness (VE) was calculated from adjusted odds ratios via multivariable logistic regression. Results Overall, 8965 ARI ED visits/hospitalizations with RSV testing were included; 7.8% of patients were RSV positive, among whom 0.3% had received RSVpreF, compared with 3.6% of controls. The adjusted VE was 92% (95% confidence interval, 64%–98%). We estimated similar VE among patients with risk conditions (92% [95% confidence interval: 65%–98%]), the oldest subgroup (age ≥75 years; 95% [60%–99%]), those with critical outcomes (intensive care unit admission, mechanical ventilation, respiratory failure, vasopressor use, or death; 90% [16%–99%]), and those with severe disease (defined as ED visit or hospitalization requiring oxygen; 92% [35%–99%]). Conclusions Among older adults, RSVpreF demonstrated high VE against RSV-related ARI hospitalization or ED visits, including among high-risk subgroups, and against severe outcomes. RSV vaccination programs can protect groups at the highest risk of severe disease.