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Flu Pandemics »
Pandemic Flu Outbreak
An influenza pandemic is a global outbreak of disease that occurs
when a new influenza A virus appears or “emerges” in the
human population, causes serious illness, and then spreads easily from
person to person worldwide. Pandemics are different from seasonal outbreaks
or “epidemics” of influenza. Seasonal
outbreaks are caused by subtypes of influenza viruses that already
circulate among people, whereas pandemic outbreaks are caused by new
subtypes, by subtypes that have never circulated among people, or by
subtypes that have not circulated among people for a long time. Past
influenza pandemics have led to high levels of illness, death, social
disruption, and economic loss.
During the 20th century, the emergence of several new influenza A virus
subtypes caused three pandemics, all of which spread around the world
within a year of being detected.
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1918-19, "Spanish
flu," [A (H1N1)], caused the highest number of known influenza
deaths. (However, the actual influenza virus subtype was not detected
in the 1918-19 pandemic). More than 500,000 people died in the United
States, and up to 50 million people may have died worldwide. Many
people died within the first few days after infection, and others
died of secondary complications. Nearly half of those who died were
young, healthy adults. Influenza A (H1N1) viruses still circulate
today after being introduced again into the human population in 1977.
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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.
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1968-69, “Hong Kong flu," [A (H3N2)],
caused about 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. Influenza A (H3N2) viruses still circulate today.
Both the 1957-58 and 1968-69 pandemics were caused by viruses containing
a combination of genes from a human influenza virus and an avian influenza
virus. The 1918-19 pandemic virus appears to have an avian origin. |
