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. Author manuscript; available in PMC: 2009 May 29.
Published in final edited form as: Nature. 2008 Apr 16;453(7195):615–619. doi: 10.1038/nature06945

Figure 2. A ‘source-sink’ model for the evolution of influenza A virus.

Figure 2

Viral genetic and antigenic diversity (shown by different colours) is continuously generated in a reservoir, or ‘source’ population, perhaps represented by the tropics, before being exported to ‘sink’ populations in the Northern and Southern Hemispheres as shown by the arrows. The continuous transmission of influenza A virus in the source population, and hence its larger effective population size, allows natural selection for antigenic diversity to proceed more efficiently than in the sink populations that are afflicted by major seasonal bottlenecks.