Understanding Seasonal, Avian and Pandemic Influenza

Understanding Seasonal, Avian and Pandemic Influenza

Influenza is a respiratory illness caused by a virus that causes fever, headache, body ache, cough and extreme tiredness in people.


Seasonal influenza, also known as the common flu, occurs every year.  It is a significant health problem, but not a disaster.  Each year, 10-20% of the US population becomes ill with the flu and about 36,000 people die from the flu or its complications. Most people have some immunity to the virus, and vaccines are available to prevent people from becoming infected.  You can get a flu vaccine from your doctor, the Public Health Department, and other locations during the fall months.

Avian (or bird) flu is caused by influenza viruses that occur naturally among wild birds.  There are several types of avian flu that commonly circulate in the bird population.  Many of them don’t represent any significant threat to humans.  H5N1 is a type of bird flu that has caused health experts to become concerned.  H5N1 is deadly to domestic fowl and has been infrequently transmitted from birds to humans.  There may have been extremely rare person-to-person transmission.  Some experts believe that the H5N1 virus could be the virus that causes the next flu pandemic.


A pandemic is a global disease outbreak. A flu pandemic occurs when a new influenza virus emerges for which people have little or no immunity, and for which there is no vaccine. The disease spreads easily person-to-person, causes serious illness and can sweep across the country and around the world in very short time.  History suggests that influenza pandemics have probably happened during at least the last four centuries. Since 1900, three pandemics have occurred: 


·              1918 (Spanish Flu): It is estimated that approximately 20 to 40 percent of the worldwide population became ill and that over 50 million people died. Between September 1918 and April 1919, approximately 675,000 deaths from the flu occurred in the U.S. alone.

·              1957 (Asian Flu): Although the Asian flu pandemic was not as devastating as the Spanish flu, about 69,800 people in the U.S. died.

·              1968 (Hong Kong Flu): The number of deaths between September 1968 and March 1969 for this pandemic was 33,800, making it the mildest pandemic in the 20th century.


While it is difficult to predict when the next influenza pandemic will occur, or how severe it will be, health professionals are concerned that the continued spread of a highly pathogenic avian H5N1 virus across eastern Asia and other countries represents a significant threat to human health, as it may evolve into a strain that can be easily spread from person to person.  


For a pandemic to take place, the H5N1 virus would need to improve its transmissibility among humans. This could occur in two ways: 1) Genetic material may be exchanged between human and avian viruses during co-infection (infection with both viruses at the same time) of a human or another mammal. 2) A more gradual process is when the capability of a virus to bind to human cells increases during infections of humans.  Either method could result in fully transmissible pandemic virus.




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