Which strain of the flu was responsible for more than 20 million deaths in 1918 worldwide?
The correct answer and explanation is:
Correct Answer: The H1N1 influenza A virus strain was responsible for the 1918 flu pandemic, also known as the Spanish flu, which caused more than 20 million deaths worldwide.
Explanation (300 words):
The 1918 influenza pandemic, commonly referred to as the Spanish flu, was caused by the H1N1 strain of the influenza A virus. It was one of the deadliest pandemics in human history, infecting an estimated 500 million people — about one-third of the global population at the time — and resulting in more than 20 million deaths, with some estimates reaching as high as 50 million or more.
What made the 1918 flu particularly devastating was its unusual mortality pattern. Unlike typical influenza outbreaks that primarily affect the very young and the elderly, the Spanish flu had a high fatality rate among young adults aged 20 to 40. This anomaly has been attributed to a phenomenon known as a cytokine storm — an overreaction of the body’s immune system that proved deadly in individuals with strong immune responses.
The H1N1 virus of 1918 was highly contagious and virulent, spreading rapidly due to conditions of World War I: overcrowded military camps, mass troop movements, and poor hygiene. The war also suppressed information in some countries, allowing the virus to spread unchecked. Spain, being neutral in the war, had a free press that reported openly on the outbreak, which is why the pandemic was dubbed the “Spanish flu,” though it did not originate there.
Modern studies, including the analysis of preserved lung tissues and reconstructed virus samples, have confirmed that the 1918 strain was indeed an avian-origin H1N1 virus. Lessons from this pandemic have greatly influenced modern public health strategies and pandemic preparedness efforts, including the development of flu vaccines and the importance of global disease surveillance systems.