The origins of pandemic influenza ? a perspective

Abstract

Following the isolation of the first human influenza virus in 1933, there have been two Type A influenza pandemics. One was the Asian influenza pandemic in 1957, when an H2N2 virus replaced the H1N1 viruses then circulating, and the other was in 1968 when the Hong Kong H3N2 virus replaced the H2N2 viruses. The H1N1 virus that re-emerged in 1977 did cause a worldwide epidemic (or pandemic) but this virus is not considered by many people to be a true ?pandemic? virus.