Investigating Respiratory Viruses in the Acutely Ill (IVY) Network
The Investigating Respiratory Viruses in the Acutely Ill (IVY) network currently consists of 25 medical centers in 20 U.S. states. Prior to December 2022, the network was known as the “Influenza and Other Viruses in the Acutely Ill network.” IVY was created initially in 2019 to estimate how well influenza (flu) vaccines work to prevent severe flu illness among intensive care unit (ICU) patients. In 2021, IVY expanded to also assess how well flu vaccines work to prevent flu hospitalizations and how well COVID-19 vaccines work to prevent COVID-19 hospitalizations. In 2022, patients hospitalized with respiratory syncytial virus (RSV) were added to begin monitoring RSV disease among hospitalized adults.
Flu Vaccine Effectiveness
Measuring vaccine effectiveness (VE) in hospitalized adults is important to better understand how well flu and COVID-19 vaccines protect against hospitalizations and ICU admissions. VE among adults 65 years and older is especially important because this group of people has the highest flu- and COVID-19-associated hospitalization rates compared to other age groups.
CDC measures VE to evaluate the benefits of flu and COVID-19 vaccines in different age groups and against different clinical outcomes, such as hospitalization or ICU admission. These efforts help convey the importance and impact of flu vaccination and COVID-19 vaccination.
Sites and Study Design
25 participating sites are located in 20 U.S. states:
- Baylor Scott & White Medical Center (Texas)
- Baylor University Medical Center (Texas)
- Baystate Medical Center (Massachusetts)
- Beth Israel Deaconess Medical Center (Massachusetts)
- Cleveland Clinic (Ohio)
- Emory University Medical Center (Georgia)
- Hennepin County Medical Center (Minnesota)
- Henry Ford Health (Michigan)
- Intermountain Medical Center (Utah)
- Johns Hopkins Hospital (Maryland)
- Montefiore Medical Center (New York)
- The Ohio State University Wexner Medical Center (Ohio)
- Oregon Health & Science University Hospital (Oregon)
- Stanford University Medical Center (California)
- UCLA Medical Center (California)
- University of Colorado Hospital (Colorado)
- University of Iowa Hospitals (Iowa)
- University of Miami Medical Center (Florida)
- University of Michigan Hospital (Michigan)
- University of Washington (Washington)
- Vanderbilt University Medical Center (Tennessee)
- Wake Forest University Baptist Medical Center (North Carolina)
- Barnes-Jewish Hospital (Missouri)
- University of Arizona Medical Center (Arizona)
- Yale University (Connecticut)
IVY uses a test-negative observational study design and collects data at participating hospitals.
- More information about how CDC’s VE studies are conducted and how to interpret results is available at How Flu Vaccine Effectiveness and Efficacy are Measured: Questions and Answers for Health Professionals.
- Seasonal Influenza Vaccine Effectiveness Studies show the overall adjusted VE and related references for each season starting in 2004-2005.