Pandemic flu A nurse takes a patient’s pulse in the influenza ward at Walter Reed Hospital in Washington, D.C., near the end of the Spanish Flu epidemic, Nov. 1, 1918. Fresh air was believed to help prevent the spread of the disease, which killed 50 million to 100 million people worldwide. Pandemic flus such as this are rare, occurring just three times in the 20th century, according to the Centers for Disease Control and Prevention. Library of Congress photo SHARE: Download: Full Size (0.04 MB) Credit: Library of Congress VIRIN: 181101-O-ZZ999-001.JPG Photo Gallery