The impact of seasonal flu—and of vaccinations

The way seasonal flu impacts the United States changes each year, but the cumulative effect remains considerable. In reviewing the incidence of seasonal influenza between 2010 and 2016, the Centers for Disease Control and Prevention (CDC) found that on average, about 8% of the national population gets sick from the seasonal flu; these numbers may fluctuate between 3% and 11% each year.

Most people recover from the flu within a few days to a couple of weeks. However, millions with seasonal influenza end up visiting a healthcare provider; tens of thousands are hospitalized, and a smaller but notable number of people die from it. These flu cases, flu-related medical visits, hospitalizations and deaths that occur in one flu season make up the burden of influenza on the United States.

Each year, the CDC collects data relevant to the burden of flu through networks of state and local health departments that perform population-based surveillance across the country. Using these numbers in mathematical models, the CDC creates preliminary estimates on the total number of influenza cases, as well as flu-related medical visits, hospitalizations and deaths. The numbers generated by the CDC on the burden of influenza after each flu season may shift, as it takes about two years before data related to flu testing becomes final.