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Disease Burden of Influenza

The severity of influenza disease in the United States can vary widely and is determined by a number of factors including the characteristics of circulating viruses, the timing of the season, how well the vaccine is working to protect against illness, and how many people got vaccinated. CDC tracks severity principally through its national Influenza Surveillance System that monitors key indicators like the percentage of deaths resulting from pneumonia or influenza, rates of influenza-associated hospitalizations, pediatric deaths and the percentage of visits to outpatient clinics for influenza-like illness. CDC then applies a statistical methodology to those data to classify severity as being low, moderate, high or very high. CDC also uses mathematical models to fill in the pyramid of the disease burden (see figure below) and estimate the impact of influenza immunization programs. Models are used to augment surveillance data because most of the surveillance systems only look at portions of the U.S. population and in some instances there can be significant under-reporting of influenza deaths and hospitalizations. This page includes links to key resources on the burden of influenza.

This image shows a pyramid with the range of flu cases, hospitalizations and deaths estimated annually in the United States since 2010. At the bottom of the pyramid is the numbers of flu cases, which is greatest (between 9.2 million and 60.8 million illnesses), followed by hospitalizations (between 140,000 and 710,000 hospitalizations), followed by deaths (between 12,000 and 56,000 deaths).

While the impact of flu varies, it places a substantial burden on the health of people in the United States each year. CDC estimates that influenza has resulted in between 9.2 million and 35.6 million illnesses, between 140,000 and 710,000 hospitalizations and between 12,000 and 56,000 deaths annually since 2010.

Flu-related Illness and Hospitalization

Flu-related illness and hospitalization averted by vaccination
2016-2017 season
2015-2016 season
2014-2015 season
2013-2014 season
2012-2013 season
2011-2012 season
2005-2011 seasons

Economic Impact of Influenza