Influenza pandemics

Abstract

The recent H1N1 pandemic that emerged in 2009 has illustrated how swiftly a new influenza virus can circulate the globe. Here we explain the origins of the 2009 pandemic virus, and other twentieth century pandemics. We also consider the impact of the 2009 pandemic in the human population and the use of vaccines and antiviral drugs. Thankfully this outbreak was much less severe than that associated with Spanish flu in 1918. We describe the viral factors that affect virulence of influenza and speculate on the future course of this virus in humans and animals.

Fig. 1

Schematic cross section of the influenza A virus

Fig. 2

A time line illustrating the emergence of the three twentieth century influenza pandemic subtypes. The H1N1 virus accepted alternative genes in recombination events with avian viruses, giving rise to the H2N2 and H3N2 subtypes

Fig. 3

Influenza-like illness incidence in England and Wales since the Hong Kong pandemic [46]

Fig. 4

The emergence of the pH1N1 2009 influenza virus. A series of avian viruses transferred into swine hosts. There multiple recombination events of classical swine influenza (black) resulted in a triple reassortant (TRIG), when recombined with Eurasian swine influenza (grey) generated the pH1N1 virus [51]

Fig. 5

A schematic representing the putative sialic acid linked receptor distribution on cells in the human upper airway, the avian gut and the swine respiratory system, with cognisant avian-like or human-like HA attachment proteins