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Tuesday, May 05, 2009

A brief history of pandemic influenza

Further to our previous discussion on swine flu, this article explores the history of pandemic influenza.


A pandemic is a massive viral outbreak, which affects large amounts of people over a wide geographic area. People usually have little or no immunity to pandemic outbreaks, which results in high death rates. Most pandemics have been caused by a new strain of the influenza virus, which is often the result of an animal virus mutating into one that can infect humans. We are exposed to influenza viruses many times throughout our lives and we have built up an immunity to lots of them. We have not built up an immunity, however, to new strains that jump from animals to humans. This type of situation creates the potential for an outbreak that could kill many people. The process of a virus jumping from animals to humans usually occurs when an avian virus infects swine. Since pigs and humans have similar DNA, the virus has the potential to mix with other pig viruses and mutate into something that can infect humans as well. The current swine flu outbreak is an example of this process.

Pandemics have been occurring throughout history. It is generally accepted that pandemics will occur three to four times every century, although scientists don't seem to know why this pattern exists. A brief history of pandemic influenza can be seen in the timeline below.


The first significant pandemic dates all the way back to the Peloponnesian War in 430 BC. In the last century, there were three pandemics: the Spanish Flu of 1918 and 1919, the Asian Flu of 1957 and 1958, and the Hong Kong Flu, which occurred between 1968 and 1969. The most severe pandemic was the Spanish Flu, which struck at the end of World War I and was estimated to have killed between 20 and 40 million people worldwide and between 30 and 50 thousand people in Canada. This pandemic was caused by a strain of influenza known as H1N1, which had an attack rate of 25 per cent. While most of the time influenza is especially harmful to the elderly, this outbreak was characterized by a high death rate among younger people. The Canadian government's response to the Spanish Flu was practically nonexistent. According to author Eileen Pettigrew:

Parliament was not sitting during the epidemic, and to my disappointment I found almost nothing relevant in the papers of Prime Minister Robert Laird Borden. He had gone to Britain in November 1918 to head the Canadian delegation to the Peace Conference, and when he returned to Canada the following May, the worst was over in southern Canada.

The other two pandemics caused significantly less damage than the Spanish Flu. The Asian Flu, or the H2N2 strain, had an attack rate of approximately 25 to 30 per cent. It infected between 10 and 35 per cent of the world's population and killed approximately 1 million people. The Hong Kong Flu was the lightest of the three pandemics. This strain was known as H3N3 and was responsible for killing about 700,000 people worldwide. This virus had an attack rate of between 20 and 35 per cent.

Posted by Jesse Kline on May 5, 2009 in Current Affairs | Permalink


So, to help keep these things in perspective, even with the Spanish Flu (the worst flu pandemic in recent memory), the survival rate for those who contracted it was between 95% and 97.5% (according to Wikipedia).

Posted by: Anonymous | 2009-05-06 8:36:46 AM

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