Influenza surveillance.
D000368:Aged; D003430:Cross-Sectional Studies; D004196:Disease Outbreaks; D004739:England / Q000453:epidemiology; D006801:Humans; D015994:Incidence; D009980:Influenza A virus; D007251:Influenza, Human / Q000453:epidemiology*; D011159:Population Surveillance; D014852:Wales / Q000453:epidemiology