Seasonal Flu vs Pandemic Flu

Pandemic flu

What Is a Flu Pandemic?

A pandemic is a global disease outbreak. An influenza pandemic occurs when a new influenza Type A virus emerges for which there is little or no immunity in the human population. Next, it begins to cause serious illness and spreads easily from person to person worldwide. A pandemic is determined by the spread of disease, not its ability to cause death.

Pandemic flu is different from seasonal flu.

Seasonal Flu Pandemic Flu
Outbreaks follow predictable seasonal patterns; occurs annually, usually in winter, in temperate climates. Occurs rarely (three times in the 20th century).
Usually some immunity built up from previous exposure. No previous exposure; little or no preexisting immunity.
Healthy adults usually not at risk for serious complications; the very young, the elderly, and those with certain underlying health conditions at increased risk for serious complications. Healthy people may be at increased risk for serious complications.
Health systems can usually meet public and patient needs. Health systems may be overwhelmed.
Vaccine developed based on known flu strains and available for annual flu season. Vaccine probably would not be available in the early stages of a pandemic.
Adequate supplies of prescription flu medicines are usually available. Effective prescription flu medicines may be in limited supply.
Between 3,000 and 49,000 people in the U.S. die from seasonal flu annually. Number of deaths could be quite high (eg, US 1918 death toll was approximately 675,000).
Symptoms: fever, cough, runny nose, muscle pain. Deaths often caused by complications, such as pneumonia. Symptoms may be more severe and complications more frequent.
Generally causes modest impact on society (eg, some school closings, people who are sick advised to stay home). May cause major impact on society (eg, widespread restrictions on travel, closing of schools and businesses, cancellation of large public gatherings).
Manageable impact on domestic and world economy. Potential for severe impact on domestic and world economy.

Adapted from information at

Historically, the 20th century saw three pandemics of influenza, and the 21st has experienced one flu pandemic.


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