Table 1.

Influenza pandemic of the 20th century.

Date	Strain	Estimate number of worldwide deaths	Comments
1918-1919 (Spanish Flu)	H1N1	Over 50 million	Three waves: A first, mild wave in the spring of 1918 was replaced by a second wave in September to November, 1918 that resulted in a mortality rate of over 2.5%. A third wave with equally high mortality rates swept around the world in 1919. The virus probably originated from the United States and then spread to Europe.
1957-1958 (Asian Flu)	H2N2	1-1.5 million	Two waves: The virus originated in Southern China in February 1957 and spread over 3 months to Singapore, Hong Kong and Japan and in October 1957 reached the United Kingdom and United States. A second wave was detected in January 1958.
1968-1969 (Hong Kong Flu)	H3N2	¾ million	Two waves in the winters of 1968-1969 and 1969-1970. The virus originated from Hong Kong in July 1968.