A landmark multi-state study led by the Centers for Disease Control and Prevention's VISION Network has delivered the most comprehensive assessment to date of 2023-2024 COVID-19 vaccine effectiveness among U.S. adults during the XBB and JN.1 Omicron subvariant waves. The research demonstrates that updated COVID-19 vaccines provide substantial protection against severe illness, with critical illness risk reduced by 48% during the first seven to 299 days after vaccination.
Robust Protection Against Severe Outcomes
The study, spanning more than 345,000 emergency department and urgent care encounters and over 111,000 hospitalizations across 230 hospitals and 362 emergency departments and urgent care centers, revealed significant protective benefits. Updated vaccines reduced the risk of emergency department and urgent care visits related to COVID-19 by 24%, hospitalizations by 29%, and critical illness—defined as intensive care unit admission or in-hospital death—by 48%.
"These results are both reassuring and instructive for patient care," said study co-author Shaun Grannis, M.D., M.S., vice president for data and analytics at Regenstrief Institute and professor at Indiana University School of Medicine. "This study demonstrates that the updated COVID-19 vaccines continue to offer significant protection against severe outcomes like hospitalization and critical illness, especially in the months immediately following vaccination."
Peak Protection and Waning Immunity
Maximum protection against all measured COVID-19 outcomes was observed during the first two months after vaccination, with severe case reduction reaching up to 68% against critical illness. However, vaccine effectiveness waned over time, particularly beyond six months after vaccination, highlighting the importance of timely booster administration.
The research was conducted through the CDC's VISION Network in collaboration with healthcare systems across seven states, including Kaiser Permanente Northwest, University of Colorado, Intermountain Health, HealthPartners, Kaiser Permanente Northern California, and Regenstrief Institute. This broad geographic representation ensured robust analysis across diverse medical facilities in both urban and rural areas.
Comprehensive Study Design
VISION investigators evaluated electronic health record data integrated with laboratory and vaccination records from September 21, 2023, to August 22, 2024. The research focused on adults aged 18 years and older, examining outcomes among those who did and did not receive the 2023-2024 monovalent XBB.1.5 COVID-19 vaccines during periods when both XBB and JN.1 Omicron variants were predominant.
"This study offers encouraging news for population health," said co-author Brian Dixon, PhD, MPA, director of the Regenstrief Center for Biomedical Informatics and professor at IU Indianapolis Fairbanks School of Public Health. "Our findings show that the updated COVID-19 vaccines continue to provide protection against severe illness and hospitalization. Effective vaccines remain a critical tool in keeping communities healthy and reducing costs associated with COVID-19 infection by preventing hospitalizations and emergency department visits."
Critical Protection for Vulnerable Populations
The findings underscore the additional protection provided by updated COVID-19 vaccines above and beyond previous infection or vaccination. While protection against mild and moderate illness decreased over time, the vaccine continued to offer strong defense against critical illness throughout the study period. Protection was especially significant for adults 65 and older, supporting current public health guidance that recommends timely vaccination and additional doses for high-risk groups.
The study highlights the importance of following CDC recommendations for updated COVID-19 vaccination, particularly in light of waning immunity and continuing virus evolution. The research reinforces that receiving updated COVID-19 vaccines remains crucial, especially for older adults and those at increased risk for severe outcomes.
The study, titled "Estimated 2023-2024 COVID-19 Vaccine Effectiveness in Adults," was funded by the CDC and published in JAMA Network Open, representing a collaborative effort among leading health systems and public health institutes across the United States.
