P-2069. Updated 2023–2024 (Monovalent XBB.1.5) COVID-19 Vaccine Effectiveness Against COVID-19–associated Hospitalization Among Adults — IVY Network, 20 U.S. States

Abstract Background On September 12, 2023, the Advisory Committee on Immunization Practices recommended updated 2023–2024 (Monovalent XBB.1.5) COVID-19 vaccination for all persons aged ≥6 months to prevent COVID-19. Few data are available on the effectiveness of updated 2023–2024 COVID-19 vaccine against COVID-19–associated hospitalization among adults, particularly in high-risk groups, including older adults, persons with comorbidities, and immunocompromised persons. Methods Data from the Investigating Respiratory Viruses in the Acutely Ill (IVY) Network were used to conduct a case-control analysis estimating updated 2023–2024 COVID-19 vaccine effectiveness (VE) against COVID-19–associated hospitalization. During September 21, 2023–March 31, 2024, adults aged ≥18 years with COVID-19-like illness were enrolled at 26 hospitals in 20 U.S. states. COVID-19 case patients tested positive for SARS-CoV-2 by a nucleic acid or antigen test within 10 days of illness onset, while control patients tested negative for SARS-CoV-2. VE was estimated using multivariable logistic regression comparing the odds of receipt of an updated 2023–2024 COVID-19 vaccine dose versus no updated dose among case and control patients. VE models were adjusted for age, sex, race and ethnicity, admission date, and geographic region. Results were stratified by age, Charlson Comorbidity Index (CCI) score, and immunocompromised status. Results A total of 7843 adults were enrolled, including 2090 COVID-19 case patients and 5753 control patients. Among immunocompetent adults, VE against COVID-19–associated hospitalization was 41% (95% CI=28%–51%, median time since updated dose = 73 days) among persons aged ≥18 years, 48% (95% CI=19%–66%) among persons aged 18–64 years, 42% (95% CI=27%–53%) among persons aged ≥65 years, 42% (95% CI=22%–57%) among persons with CCI < 5, and 41% (95% CI=23%–54%) among persons with CCI ≥5 (Figure). Among immunocompromised adults, VE against COVID-19–associated hospitalization was 25% (95% CI=0%–44%, median time since updated dose = 74 days). Conclusion Updated 2023–2024 COVID-19 vaccination provided protection against COVID-19–associated hospitalization among immunocompetent adults. VE was similar across age groups and CCI scores, but may be lower among immunocompromised adults. Disclosures Adam S. Lauring, MD, PhD, Roche: Advisor/Consultant Ithan Peltan, MD, Bluejay Diagnostics: Grant/Research Support|Regeneron: Grant/Research Support Nicholas Mohr, MD, Endpoint Health: Grant/Research Support Steven Chang, MD, PhD, Kiniksa: Consulting fee Christopher Mallow, MD, Medical Legal Consulting: Advisor/Consultant Ivana Vaughn, PhD, eMax Health Systems, LLC: Grant/Research Support|Evidera, Inc: Grant/Research Support