165. Real-world Abrysvo Vaccine Effectiveness (VE) against Respiratory Syncytial Virus (RSV)-related Severe Acute Respiratory Infection (ARI) Hospitalizations and Emergency Department (ED) Visits—Kaiser Permanente of Southern California (KPSC), November 2023–April 2024
Authors: Tartof Sara Y , Aliabadi Negar , Goodwin Gabriella , Slezak Jeff , Hong Vennis , Ackerson Bradley , Ackerson Bradley , Liu Qing , Shaw Sally , Welsh Sabrina , Stern Julie , Kapadia Banshri , Spence Brigitte , Lewnard Joe , Davis Gregory , Aragones Michael , Dutro Michael , Chilson Erica , Gonzalez Elisa , Hubler Robin , Miller Ashley , Chia Brandon , Jodar Luis , Gessner Bradford D , Begier Elizabeth 
Published: January 2025

Abstract

Background
Abrysvo’s pivotal trial analysis of efficacy against severe RSV-related respiratory disease was hampered by accrual of few hospitalizations/ED events. In this post-licensure study, we evaluated Abrysvo VE against 1st RSV-related severe ARI in KPSC, a large healthcare system.

Methods
We assessed Abrysvo VE among adults aged ≥ 60 years through KPSC members’ electronic health records plus enhanced specimen testing using a test-negative case-control study (study period: 11/24/2023–4/9/2024). ARI was defined as ED/hospitalizations with an ARI ICD-10 code, with respiratory specimens tested on GenMark RP2 expanded multiplex PCR assay; severe ARI required supplemental oxygen use. Cases were defined as RSV+ ARIs. Two sets of pre-specified controls were used: ‘Strict’: RSV- and positive for a non-vaccine preventable disease (VPD), and ‘Broad’: all RSV-. The strict group accounted for lower sensitivity of RSV testing in adults and potential bias with VPD controls. Exposure was Abrysvo receipt ≥ 21 days before encounter. Odds ratios (OR) and 95% confidence intervals (CI) were estimated from multivariable logistic regression adjusted for demographic and clinical characteristics. VE (1−OR X 100%) was estimated for severe ARI, ARI hospitalization/ED visit (separately and combined), and ARI among those with high-risk conditions.

Results
Among 5,120 KPSC members in the study population, &gt; 50% were ≥ 75 years, 95% had ≥ 1 underlying comorbidities, 15% were immunocompromised. For RSV-related severe ARI (Table 1), the strict analysis included 372 cases and 496 controls; the vaccinated received Abrysvo a median of 69 days before the ARI. Adjusted VE was 91% (95% CI: 27–99). The broad analysis included 372 cases and 4,748 controls; the vaccinated received Abrysvo a median of 62.5 days before the ARI. Adjusted VE was 90% (95% CI: 26–99). Additional VE estimates ranged from 88–91% among different subsets of the ARI hospitalization/ED visit population (Table 2).

Conclusion
This study demonstrated real-world Abrysvo VE during its first 5 months of use against severe ARI in hospital/ED settings among US adults ≥ 60 years of age. These results expand on clinical trial results by including severe disease endpoints and a substantial proportion of high-risk persons.

Disclosures
Sara Y. Tartof, PhD MPH, GSK: Funding paid directly to institution; vaccines provided directly to institution|Pfizer Inc.: Funding paid directly to institution; vaccines provided directly to institution Negar Aliabadi, MD, MS, Pfizer: I am an employee of Pfizer and own stocks in the company Jeff Slezak, MS, Dynavax Technologies: Grant/Research Support|Pfizer, Inc.: Grant/Research Support Qing Liu, M.S., Pfizer Inc: Stocks/Bonds (Public Company) Michael Dutro, PharmD, Pfizer: Employee|Pfizer: Stocks/Bonds (Public Company) Erica Chilson, PharmD, Pfizer, Inc: Employee|Pfizer, Inc: Stocks/Bonds (Public Company) Elisa Gonzalez, MS, Pfizer: Stocks/Bonds (Private Company) Ashley Miller, MA, CCRP, Pfizer: Stocks/Bonds (Public Company) Bradford D. Gessner, M.D., M.P.H., Pfizer: Employee|Pfizer: Stocks/Bonds (Public Company) Elizabeth Begier, MD, M.P.H., Pfizer: Employee|Pfizer: Stocks/Bonds (Public Company)