CDC monitors the progress of flu season

The overall health impact (e.g., infections, hospitalizations, and deaths) from flu varies from season to season. CDC collects, compiles, and analyzes information on influenza activity year-round in the United States and produces FluView, a weekly surveillance report, and FluView Interactive, which allows for more in-depth exploration of influenza surveillance data. Both are updated each week.

The U.S. influenza surveillance system is a collaborative effort between CDC and its many partners in state and local health departments, public health and clinical laboratories, vital statistics offices, health care providers, long term care facilities, hospitals, and clinics and emergency departments. Information in five categories is collected from 10 different data sources that allow CDC to:

• Find out when and where influenza activity is occurring;
• Track influenza-related illness;
• Determine what influenza viruses are circulating;
• Detect changes in influenza viruses; and
• Measure the impact influenza is having on hospitalizations and deaths in the United States.

These surveillance components allow CDC to determine when and where flu activity is occurring, determine what types of influenza viruses are circulating, detect changes in the influenza viruses collected and analyzed, track patterns of influenza-related illness, and measure the impact of influenza in the United States.

Understanding why a week-long delay exists between flu surveillance data collection and reporting

Flu surveillance data collection is based on a reporting week that starts on Sunday and ends on the following Saturday of each week. Each surveillance participant is requested to summarize the weekly data and submit it to CDC by the following Tuesday afternoon. The data are then downloaded, compiled, and analyzed at CDC. The data are used to update FluView and FluView Interactive on the following Friday.

Other respiratory viruses

In addition to influenza viruses, several other respiratory viruses also spread during flu season and can cause symptoms similar to those seen with flu infection. These respiratory viruses include rhinovirus (one cause of the “common cold”), the virus that causes COVID-19, and respiratory syncytial virus (RSV), which is the most common cause of severe respiratory illness in young children as well as a leading cause of death from respiratory illness in those aged 65 years and older. Other commonly circulating respiratory viruses include human parainfluenza viruses (HPIV), human metapneumovirus (HMPV), respiratory adenoviruses, and human coronaviruses other than those that cause COVID-19. More information about non-influenza respiratory viruses is available.