What to know
CDC celebrated FluSurv-NET’s 20th anniversary, commemorating two decades of surveillance and rigorous scientific investigation of influenza-associated hospitalizations.
Background
CDC celebrated FluSurv-NET's 20th anniversary, commemorating two decades of surveillance and rigorous scientific investigation of influenza-associated hospitalizations. The Influenza Hospitalization Surveillance Network (FluSurv-NET) is a vital source of detailed data on flu-related hospitalizations, including demographic and clinical characteristics, underlying medical conditions, and outcomes of people hospitalized with flu. Because FluSurv-NET surveillance is population-based, the data are also used to calculate rates of flu hospitalizations (total number of flu hospitalizations/total number of people living within a specified geographic area) by age group, sex, and race and ethnicity.
The FluSurv-NET anniversary celebration marks an important milestone in recognizing the work of the surveillance network central to CDC's objective to evaluate and monitor influenza virus infections. Respiratory viruses are among the most significant causes of mortality worldwide. So far, during the 2023-2024 season, CDC estimates between 34 to 75 million flu illnesses, 15 to 33 million flu medical visits, 380,000 to 900,000 flu hospitalizations, and 17,000 to 100,000 flu deaths in the United States. FluSurv-NET data provide key inputs into developing these burden estimates.
FluSurv-NET data have not only helped estimate and monitor the severity of flu seasons and pandemics, but it has done so quickly, in near real-time. Before FluSurv-NET, data on flu were obtained through national hospital discharge data, but getting the information was slow and cumbersome. Throughout its 20-year history, FluSurv-NET's data have provided critical information on the different segments of the U.S. population impacted by flu. The network has described characteristics of special populations hospitalized with flu and helped guide policy to inform recommendations for influenza treatment and vaccination. In 2010, FluSurv-NET data influenced changes to policy, including the recommendation of flu vaccination for all persons six months and older.
Contributing to flu research through 60 high-impact publications and over 20 publications since 2020, FluSurv-NET was one of the first platforms to publish data showing that flu vaccination helps reduce serious flu illness in hospitalized people who had been vaccinated. These data helped inform the creation of the 2023 Wild to Mild campaign, an educational campaign based on the premise that even if you get flu despite getting vaccinated, the vaccine can help make your illness milder.
FluSurv-NET’s Unique Role
FluSurv-NET is an important CDC data source for describing and characterizing health disparities among racial and ethnic groups. The network collects data to assess racial and ethnic disparities in population-based rates of influenza-associated hospitalizations, ICU admissions, and deaths. FluSurv-NET has helped to show that people who are Hispanic, Black, American Indian, and Alaska Native have higher flu-related hospitalization rates than people who are White.
With funding exceeding $100 million over the past 20 years to create a robust population-based flu surveillance system, FluSurv-NET significantly contributed to U.S. public health infrastructure and ensured meaningful improvements to flu research and Americans' lives. The network provides influenza surveillance data, and users can analyze flu activity across different demographic groups and regions.
FluSurv-NET data have also been used to show how antiviral treatment reduces flu severity, including hospital length of stay and other severe outcomes. The network's data contribute to a better understanding of influenza's impact on pregnant people, children, immunocompromised persons, and other special populations.
The origins of FluSurv-NET date back to the 2003-2004 flu season, when it was established within the Emerging Infections Program (EIP) within NCEZID. It was created to track and respond to increasing flu-related pediatric deaths. By the 2004-2005 season, the network had evolved to include all ages.
In 2010, following the 2009 influenza A H1N1 pandemic, and with a need to broaden the geographic distribution, additional sites were added through a partnership with CSTE; together, the EIP sites plus the CSTE-supported Influenza Hospital Surveillance Program (IHSP) sites collectively became known as FluSurv-NET. During the COVID-19 pandemic in 2020, CDC leveraged FluSurv-NET to create COVID-NET, which monitored COVID-19-associated hospitalizations, making it one of the only systems gathering population-level data in near-real time during the pandemic. The FluSurv-NET platform was also the model for establishing a respiratory syncytial virus hospitalization surveillance system (RSV-NET). Together, FluSurv-NET, COVID-NET, and RSV-NET are collectively known as the Respiratory Virus Hospitalization Surveillance Network or RESP-NET.
As CDC celebrates FluSurv-NET's 20-year contributions to the field of influenza and its service to the U.S. population, it also acknowledges the work of the FluSurv-NET team within the Influenza Division and the long-standing collaboration with EIP and CSTE as well as the invaluable contributions from the principal investigators, surveillance officers, and other staff members from the 14 states who participate in FluSurv-NET.
Thanks to FluSurv-NET—which covers more than 30 million people, an estimated 9 percent of the U.S. population—CDC has a critical source of data with the adaptability needed to confront future pandemics.