The Spanish flu pandemic of 1918 came in three waves. When the first wave crept up in New York City during the spring, residents and officials alike saw it as just another round of the seasonal flu. By mid-summer, the number of related deaths waned, and that first wave barely received a mention in the health department’s weekly bulletins.
A century later, though, historians remember the 1918 Spanish flu as the “mother of all pandemics.” In the months after the first wave, it went on to kill an estimated 50 million to 100 million people worldwide. That surpasses the 20 million deaths reported during World War I, which was just coming to an end, and the 35 million HIV-related deaths over the last 40 years. It remains one of the most overlooked medical events in history, though its lessons still inform how public health crises are handled today.