The 1918 influenza pandemic, also known as the Spanish flu and the great influenza pandemic, was a deadly pandemic that took place more than 100 years ago. It was caused by the H1N1 influenza A virus, which was particularly deadly that year. Even though it is difficult to track the number of people who got a disease so long ago, it is estimated that 500 million people contracted the Spanish Flu during the course of the pandemic, which lasted approximately two years. This is estimated to be one-third of the global population. The virus is estimated to have killed between 25 million and 50 million people, which leads to a mortality rate of approximately 5 to 10 percent.
Like the flu today, the Spanish Flu was largely a respiratory virus. Therefore, a significant number of people died due to respiratory distress; however, the Spanish Flu also killed people due to something called cytokine storm. Some people who contracted the Spanish Flu produced an overwhelming immune response that led to widespread inflammation throughout the body. As a result, the body would have a difficult time continuing to function, leading to severe organ dysfunction. Ultimately, without the tools we have from modern medicine today, people who contracted the Spanish Flu would pass away.
Not every country kept records of how many people contracted and died of the Spanish Flu. India was hit particularly hard, where between 12 and 17 million people died. This represented approximately five percent of the population. In Finland, approximately 210,000 people were infected, and about 20,000 people died. In Sweden, approximately 34,000 people died. In Japan, approximately 23 million people were infected with the Spanish flu, and approximately 390,000 people died. In Samoa, close to a quarter of the 38,000 people died in a span of only two months. The United States was also hit very hard. At the time, the population was approximately 105 million, and close to 30 percent of the population was infected at some point. Between 500,000 and 850,000 people died during the course of the pandemic. In Brazil, approximately 300,000 people died, including the president at the time.
There were a lot of countries all over the world that were trying to censor information related to the Spanish Flu. At the time, World War 1 was still raging, and many of the leaders throughout the world were worried that the population would turn against the war if they learned of a deadly pandemic, particularly with many soldiers traveling internationally. Therefore, the Spanish Flu was largely overlooked by people, including those living in countries that were impacted particularly hard by the war, and the history of the Spanish Flu remains supplanted by World War I, considered to be a much more impactful event than the pandemic.
Samoa lost a quarter of its population to the Spanish flu. India had between 12 and 17 million residents perish to the Spanish flu, 5% of the country's population.