A Gloucestershire GP carefully recorded the incidence of influenza in his practice over a period of nearly 30 years. Dr Hope-Simpson obtained a picture of the timing and intensity of these cases from 1946 to 1974.
Is it possible to compare Kilbourne’s chronological model of the spread of influenza with this data?
Such a comparison indicates that there should be evidence of the following factors influencing the final picture:
- A distinct seasonal pattern, with the highest incidence in winter.
- A series of decreases in the size of epidemic waves as the population becomes immune to one particular strain of the virus.
- The appearance of a new strain with changed antigens, meaning that the body’s defence mechanism does not recognise it. The whole process of infection should then begin again.
- The presence of more than one strain of influenza in the population at any one time.
- Newly introduced strains from other parts of the world, which can be especially virulent.