The Spanish flu, one of the most deadly diseases in the history of humankind, emerged in 1918-1920. It is estimated that it caused the death of 100 million people all over the world. There were much more victims than during WW1. Why was this disease so lethal and why did almost 5% of the world population die?
The Spanish flu was caused by the flu strain A of the subtype H1N1 one hundred years ago. In 2009 a mutated virus H1N1 known as the Swine flu reappeared. This virus was carried by pigs and was spread to humans. Some cases of human-to-human transmission were detected as well. However, the epicentre did not become so enormous like in 1918. The Spanish flu had the most tremendous effect on Spain, consequently it was named after that country. Nevertheless, it did not emerge there.
Spain was neutral in WW1 which enabled the media to inform about the pandemic. Due to the uncensored information, it appeared that Spain was the most afflicted country. However, it is highly probable that it emerged in France, Great Britain or China.
As millions of soldiers were returning home after WW1, the virus spread all over the world. Besides, travelling gained popularity and globalization began at the beginning of the 20th century. As a consequence, many people met without a developed immune system.
Similarly, the medical science was not advanced yet, there was neither vaccination nor antibiotics hundred years ago. Equally, there were no tests which would have been able to detect an unknown virus. On the whole, the knowledge of viruses was insufficient.
Comparison with contemporary diseases
The infected people usually died two days after catching the infection. Contemporary viruses have the potential to infect a large number of people but it has the most detrimental effects on the older and chronically ill. On the contrary, the Spanish flu was harmful for anyone. In fact, it afflicted the younger population. The age of 28 was average, and 20% of the infected people died.
The experts presume that the young were afflicted because they had suffered from flu H3N8 in their childhood. This type was spread around the year 1900. It is believed that the immune system evaluated the new flu virus H1N1 incorrectly. Consequently, it caused the high mortality rate of younger people.