The magnitude of variation in temperature within a year has an effect on the seasonal variations of chickenpox incidence in Japan

We investigated the epidemic pattern of chickenpox incidence among 47 prefe ctures in Japan. There were two peaks in chickenpox incidence in all prefec tures. The first peaks appear at almost the same time in a year, while the second peaks occur at different times with relatively different types of si ze and shape. The feature of the second peak might characterize the epidemi c pattern of chickenpox. We first introduced the second peak index, that is , the ratio of the difference between the incidence at the point of the sec ond peak and the minimum incidence between the first and second peaks to th e difference between the incidence at the point of the second peak and the minimum incidence in the year. There was a close correlation between the se cond peak index and the magnitude of variation in temperature within a year corresponding to the difference between the maximum and the minimum of the monthly mean of the highest daily temperature. This is the first article f ocusing on the close relationship between the second peak of epidemic patte rn of chickenpox incidence and the variation of temperature within a year.