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An influenza pandemic is a global outbreak of influenza and occurs when a new influenza A virus emerges among people, spreads, and causes disease worldwide. Past influenza pandemics have led to high levels of illness, death, social disruption and economic loss.
There were three pandemics in the 20th century. All of them spread worldwide within 1 year of being detected. They are:
- 1918-19, "Spanish flu," [A (H1N1)], caused the highest number of known flu deaths: more than 500,000 people died in the United States, and 20 million to 50 million people may have died worldwide. Many people died within the first few days after infection and others died of complications soon after. Nearly half of those who died were young, healthy adults.
- 1957-58, "Asian flu," [A (H2N2)], caused about 70,000 deaths in the United States. First identified in China in late February 1957, the Asian flu spread to the United States by June 1957.
- 1968-69, "Hong Kong flu," [A (H3N2)], caused approximately 34,000 deaths in the United States. This virus was first detected in Hong Kong in early 1968 and spread to the United States later that year. Type A (H3N2) viruses still circulate today.
Both the 1957-58 and 1968-69 pandemic viruses were a result of the reassortment of a human virus with an avian influenza virus. The origin of the 1918 pandemic virus is not clear.
Once a new pandemic influenza virus emerges and spreads, it typically becomes established among people and circulates for many years. The U.S. Centers for Disease Control and Prevention and the World Health Organization conduct extensive surveillance programs to monitor the occurrence of influenza activity worldwide, including the emergence of potential pandemic strains of influenza virus.
See also:
Draft HHS Pandemic Influenza Response and Preparedness Plan
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