For most people, influenza, or flu, causes fever, coughing, headaches, aches and pains, and fatigue. Flu illness can escalate and develop into life-threatening complications like pneumonia and respiratory failure. Each year scientists predict which strains of the flu virus are likely to affect which areas of the world. Vaccines are developed and then distributed annually to help build immunity against seasonal flu viruses so as to protect against flu and its potentially serious complications.

A flu pandemic can occur when a novel, non-human strain of the flu virus emerges, and a given population has little or no immunity against it. If the virus spreads throughout a given population and then spreads across national or geographical boundaries, it becomes a global threat— a flu pandemic.

Flu pandemics have happened four times before in recent history—in 1918, 1957, 1968, and 2009. And, the world is currently responding to the COVID-19 pandemic, and national health systems are being put to the test.

A key element of response is being able to distribute and administer vaccine efficiently and effectively. Influenza programs can support readiness now and in the future.


For more information on flu or pandemics, please visit:

9,200,000 - 35,600,000

Cases of Influenza Yearly (United States)

140,000 - 710,000

Hospitalized for Influenza Yearly (United States)

291,245 - 645,832

Deaths from Influenza Yearly (Global)

Influenza News from the CDC

CDC International Influenza Updates

CDC Seasonal Flu Updates

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