Estimated 2023-2024 COVID-19 Vaccine Effectiveness in Adults.

Link-Gelles R, Rowley EAK, Irving SA, Klein NP, Grannis SJ, Ong TC, Ball SW, DeSilva MB, Dascomb K, Naleway AL, Koppolu P, Zerbo O, Fireman B, Hansen J, Timbol J, Block L, Dixon BE, Duszynski TJ, Allen KS, Mayer D, Chavez C, Barron M, Reese SE, Chickery S, Davis JM, Ciesla AA, Mak J, Najdowski M. Estimated 2023-2024 COVID-19 Vaccine Effectiveness in Adults. JAMA Network Open. 2025 Jun 2; 8(6):e2517402, DOI: 10.1001/jamanetworkopen.2025.17402.

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Abstract:

IMPORTANCE: SARS-CoV-2 continues to evolve, population immunity changes, and COVID-19 vaccine formulas have been updated, necessitating ongoing COVID-19 vaccine effectiveness (VE) monitoring. OBJECTIVES: To evaluate the VE of 2023-2024 COVID-19 vaccines against COVID-19-associated emergency department (ED) and urgent care (UC) encounters, hospitalizations, and critical illness, including during XBB- and JN.1-predominant periods. DESIGN, SETTING, AND PARTICIPANTS: This test-negative design VE case-control study was conducted using data from September 21, 2023, to August 22, 2024, from EDs, UC centers, and hospitals in 6 US health care systems. Eligible adults 18 years or older with COVID-19-like illness and molecular or antigen testing for SARS-CoV-2 were studied. Case patients were those with a positive molecular or antigen test result; control patients were those with a negative molecular test result. EXPOSURE: Receipt of 2023-2024 (monovalent XBB.1.5) COVID-19 vaccination with products approved or authorized for use in the US. MAIN OUTCOMES AND MEASURES: Main outcomes were COVID-19-associated ED and UC encounters, hospitalizations, and critical illness (admission to the intensive care unit or in-hospital death). VE was estimated comparing the odds of receipt of the 2023-2024 COVID-19 vaccine with no receipt among case and control patients. RESULTS: Among 345 639 eligible ED and UC encounters in immunocompetent adults 18 years or older with COVID-19-like illness and available test results (median [IQR] age, 53 [34-71] years; 209 087 [60%] female), 37 096 (11%) had a positive SARS-CoV-2 test result. VE against COVID-19-associated ED and UC encounters was 24% (95% CI, 21%-26%) during 7 to 299 days after vaccination. Among 111 931 eligible hospitalizations in immunocompetent adults 18 years or older with COVID-19-like illness and available test results (median [IQR] age, 71 [58-81] years), 10 380 (9%) had a positive SARS-CoV-2 test result. During 7 to 299 days after vaccination, VE was 29% (95% CI, 25%-33%) against COVID-19-associated hospitalization and 48% (95% CI, 40%-55%) against COVID-19-associated critical illness. VE was highest 7 to 59 days after vaccination (VE against ED and UC encounters 49%; 95% CI, 46%-52%; hospitalization, 51%; 95% CI, 46%-56%; critical illness, 68%; 95% CI, 56%-76%) and then waned (VE 180-299 days after vaccination against ED and UC encounters, -7% [95% CI, -13% to -2%]; hospitalization, -4% [95% CI, -14% to 5%]; and critical illness, 16% [95% CI, -6 to 34%]). CONCLUSIONS AND RELEVANCE: In this case-control study of VE, 2023-2024 COVID-19 vaccines were estimated to provide additional effectiveness against medically attended COVID-19, with the highest and most sustained estimates against critical illness. These results highlight the importance of receiving recommended COVID-19 vaccination for adults 18 years or older.