In 1918, the Spanish flu pandemic hit the world and became one of the worst pandemics in history.

It is estimated that approximately 20 to 40 percent of the worldwide population became ill and that over 50 million people died. During a period of the pandemic, influenza killed more people in 24 weeks than AIDS has killed in 24 years.

There were other influenza pandemics in the 20th century:

During the Asian Flu, the virus H2N2 started in China in February 1957, by June 1957 it spread to U.S. and caused 70,000 deaths in U.S.

During the Hong Kong Flu the virus H3N2 started in Hong Kong in early 1968.  Later in the year, it spread to the U.S. and caused 34,000 deaths.