Theory 28/Seasons to Years/Epidemiology
Seasonality Is Waning Against Transmission
The claim
Whether a disease is seasonal is set by the ratio of immunity waning time to the transmission season length, so fast waning produces year-round circulation at the same transmissibility.
01Mechanism
Seasonality requires susceptible accumulation during low transmission; if immunity wanes faster than the low season, susceptibles never run out.
02Prediction
Seasonality should track the ratio.
03Refutation
Seasonality tracking transmission amplitude would remove waning.