If you were to look in the dictionary under the word Ã¢â‚¬Å“pandemicÃ¢â‚¬Â you will see that a pandemic is an epidemic of global proportions, occurring over a very large area, affecting a large number of people and spreading uncontrollably among the population. Flu pandemics occur on a predictable basis, of roughly 3 times each century. Lets see what the perquisites of a flu pandemic are, how it can be stopped and what the most recent pandemics that occurred were.
Formation of Flu Pandemics
As you might know, the flu virus is one of the most rapidly evolving organisms, as it changes genetic structure almost every flu season. The amount of changes cannot be predicted and sometimes they are light, while other times they are drastic. Even more so, at some points during the virus evolution, two different strains (versions) will combine in what is known as an antigenic shift. When such a shift occurs, a new, totally different strain will emerge and its this strain that has the highest chance of starting a pandemic.
The reason for this is simple. In flu seasons when the virus doesnt modify its structure for a great amount, our bodies are more resistant to it since they are Ã¢â‚¬Å“usedÃ¢â‚¬Â to that particular structure of the virus. However, when the antigenic shift occurs, our bodies are caught totally unprepared, hence making the infection easier and the effects more dangerous.
In addition, the vaccines designed in that particular year will be less efficient. It was one of these antigenic shifts that started almost all of the great pandemics of the 20th century, including the Spanish Flu, which is probably the biggest and deadliest flu pandemic known to history.
Occurring right after the First World War has ended, in 1918, the Spanish flu was caused by the H1N1 virus strain. Over a matter of months, the flu had already killed more people than the Great War in several years of fighting. When the flu was over in 1920, the death toll reached a grim toll of 40 millions, with another 500 million being somehow infected and surviving the disease.
The next antigenic shift occurred in 1957, when the Asian Flu pandemic started. The virus causing it, the H2N2 was less powerful than its Spanish Flu version and it only took 1.5 million lives, the pandemic ending during the course of the following year. Since then, 3 more pandemics or pandemic threats occurred, but they had less lethal results:
- the Hong Kong Flu of 1968 caused by the H3N2 strain, causing 1 million deaths
- the New Jersey Swine Flu in 1976 caused by the H1N1, H1N2 and H3N2 viruses (this was not an actual pandemic, since it was stopped in time and it had a very low death toll)
- the Russian Flu of 1977 which was quelled in time
Recently, a new flu pandemic threat has risen, namely the bird flu or avian flu threat. Discovered in 1997, the new strain of virus causing it, the H5N1 has not yet evolved to a state where it can transmit itself from human to human easily (only about a dozen human-to-human cases were documented) hence it does not meet the perquisites of a pandemic. The virus evolution is carefully monitored, since the threat of a new, deadly strain is high.