Spanish Flu (1918-1919)

The 1918-1919 Spanish Flu infected 500 million people, one-third of the global population, and killed 50-100 million, disproportionately young adults aged 20-40, which is unusual compared to typical flu seasons. Its mortality rate of 2.5% was 25 times higher than the seasonal flu's 0.1%, and it killed more in a single year than World War I did in four years. The pandemic disrupted global healthcare and the 1919 Paris Peace Conference, sickening key leaders. It outperforms the 2010 Haiti earthquake in economic damage, causing $500 billion in losses (2020 USD), due to its massive scale.