Revised WHO pandemic scale requires higher incidence of disease for most alert levels.
Collier
Roger
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D004196:Disease Outbreaks / Q000145:classification*; D006801:Humans; D015994:Incidence; D053118:Influenza A Virus, H1N1 Subtype; D007251:Influenza, Human / Q000453:epidemiology* / Q000635:transmission; D018570:Risk Assessment; D014944:World Health Organization