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

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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.

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