All over the world, Spanish Influenza savaged civilian populations. One-quarter of all Americans suffered bouts of flu. About 2 percent of the entire American Indian population was killed. It then underwent several sudden and dramatic mutations in its structure. Such mutations can turn flu into a killer because its victims' immune systems have no antibodies to fight off the altered virus.
Fatal pneumonia can rapidly develop.
Deadly flu pandemics struck again in 1957 and 1968, Osterholm says. In 1975-76, international health officials were horrified to detect outbreaks of the same flu virus that had caused the 1918 nightmare. No major epidemic developed. But Osterholm is emphatic that a 1918-style horror could be repeated. Unlike modern contagious killers such as AIDS, flu is easily passed from one victim to another through the air.