It’s been 100 years since the 1918 flu pandemic swept across the globe, killing more than 50 million people, including an estimated 675,000 Americans. It was caused by an H1N1 virus with genes of avian (bird) origin, according to the Centers for Disease Control and Prevention (CDC). At the time, there was no vaccine to protect against influenza infection, and if the flu virus didn’t kill you, a secondary bacterial infection usually did as there also were no antibiotics. During this period, World War I was taking place. The conditions of World War I (overcrowding and troop movement) helped the 1918 flu spread. The vulnerability of healthy young adults, combined with the lack of vaccines and treatments, created a public health crisis.