1/3 of the world population was infected during which flu event?

• A. Flu Epidemic of 1917
• B. Measles Outbreak of the 1950s
• C. Smallpox Outbreak of the 1900s
• D. Malaria Pandemic of the 1920s

Answer: (A)

This question tests the magnitude of a global influenza outbreak. The influenza pandemic of 1918–1919, often called the Spanish flu, is estimated to have infected about one-third of the world’s population—roughly 500 million people—and caused tens of millions of deaths. That level of global spread is what makes it stand out as the flu event that reached such a vast portion of people.

The other options don’t fit because they involve diseases or outbreaks that, while serious, did not achieve that same worldwide infection rate. Measles outbreaks in the 1950s, smallpox outbreaks in the early 1900s, and a malaria situation in the 1920s did not spread globally to about one-third of the population.