The worst flu pandemic on record -- the infamous Spanish flu of 1918 and 1919 -- killed an estimated 20 million to 50 million people worldwide and some 500,000 in the United States alone, according to the Atlanta-based Centers for Disease Control and Prevention.
Within just two years, 20 percent to 40 percent of the human race was thought to have fallen ill from the virus.
Almost half of those who died in the plague -- which occurred before the development of virus-fighting vaccines -- were young and otherwise-healthy adults, according to the CDC.
A flu epidemic happens when a virus spreads rapidly through a population. This happens nearly every year. A pandemic occurs when a virus spreads across the world.
It wasn't until 1934 that scientists were able to isolate the influenza type A virus, and eventually develop vaccines in the 1940s.
Vaccinations may have prevented the 1957 Asian flu from being worse than it was. It was blamed for the deaths of about 70,000 people in the United States -- most of them elderly.
According to the CDC, the 1957 pandemic was identified quickly because of scientific advances -- also helping to prevent more deaths. Cases multiplied a great deal shortly after the original U.S. outbreak in August of that year because children spread the disease when they returned to school in the fall. The highest infection rates were among school children, young adults and pregnant women.
Flu fatalities diminished greatly by 1968, when the Hong Kong flu raced around the globe. The number of people killed in the United States in this pandemic was about 34,000, according to CDC records, making it the mildest flu pandemic of the century, according to CDC records.
Together, the Hong Kong and Asian flus caused an estimated 1.5 million worldwide deaths, according to the World Heath Organization, and cost $32 billion in health care and lost productivity.
You omitted the Swine Flu of '76.
"Within just two years, 20 percent to 40 percent of the human race was thought to have fallen ill from the virus."
And I believe that EVERYONE had been EXPOSED to it.