Updated COVID-19 vaccines found effective against severe illness

A new multi-state study led by the Centers for Disease Control and Prevention's (CDC) VISION Network – including Regenstrief Institute – has provided the most comprehensive assessment to date of the effectiveness of 2023-2024 COVID-19 vaccines among adults in the U.S. during the XBB and JN.1 Omicron subvariant waves.

Data suggest that receiving updated COVID-19 vaccines remains crucial, especially for older adults and those at increased risk for severe outcomes, and underscores the additional protection provided by the 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.

Partners for this study, in addition to the CDC and Regenstrief, include Kaiser Permanente Northwest, University of Colorado, Intermountain Health, HealthPartners and Kaiser Permanente Northern California.

These results are both reassuring and instructive for patient care. 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. These findings reinforce the importance of staying up to date with recommended vaccines, particularly for our older and more vulnerable patients as the virus continues to evolve."

Shaun Grannis, M.D., M.S., study co-author, vice president for data and analytics at Regenstrief and a professor at the Indiana University School of Medicine

The study spanned more than 345,000 emergency department (ED)/urgent care encounters and more than 111,000 hospitalizations in adults in the U.S. across 230 hospitals and 362 E.D.s and urgent care centers.

Key findings

• The updated vaccines reduced the risk of ED and urgent care visits related to COVID-19 by 24 percent, hospitalizations by 29 percent and critical illness (intensive care unit admission or in-hospital death) by 48 percent during the first seven to 299 days after vaccination.
• Maximum protection against all measured COVID-19 outcomes was observed during the first two months after vaccination, with severe case reduction of up to 68 percent against critical illness.
• Vaccine effectiveness (VE) waned over time, particularly beyond six months after vaccination.

The study was conducted through the CDC's VISION Network in collaboration with healthcare systems in Oregon and Washington (Kaiser Permanente Northwest), Colorado (University of Colorado), Utah (Intermountain Health), Indiana (Regenstrief Institute), Minnesota and Wisconsin (HealthPartners), and California (Kaiser Permanente Northern California). Regenstrief Institute contributes data and scientific expertise to the network, ensuring robust analysis across a broad range of medical facilities in urban and rural areas.

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. The study covered 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 a 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."

The findings highlight the importance of following CDC recommendations for updated COVID-19 vaccination, particularly in light of waning immunity and continuing virus evolution. 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, "Estimated 2023-2024 COVID-19 Vaccine Effectiveness in Adults," was funded by the CDC and is published in JAMA Network Open.