2009 pandemic influenza A/H1N1

Abstract

Influenza A/H1N1 has a long association with humans. An influenza A/H1N1 virus was responsible for the first and most severe pandemic of the twentieth century in 1918, and remained in continuous circulation until 1956. A/H1N1 then re-emerged in 1977 and has remained in global circulation alongside A/H3N2 viruses and influenza B until the present day; however, a pandemic was not declared in 1977, and a significant impact of the virus was only ever described in children and young adults. It is less well remembered that a different A/H1N1 of swine origin had in fact brought the world to the brink of a pandemic one year earlier in 1976. This outbreak of ‘swine flu’ in Fort Dix, USA, is covered in Chapter 17 but is the first documented occasion on which an influenza virus of swine origin has caused widespread human disease.