ILI forecasts for 2017-2018 – Epidemic Week 45

This is the third week of the CDC Flu Challenge.  Most regions (1, 2 , 4, 5, 6 and 7) and the national are well above their historic %ILI values for this time of year.  Three regions (8, 9, and 10) are at their historic average value and only one region (Region 3) is below its historic value.  Our forecast for the nation was selected from a large number of predictions based on spatially-coupled mechanistic compartmental (Susceptible-Infectious-Recovered) models that allow the force of infection to depend on the school vacation schedule and/or on the specific humidity in a particular region. Our prediction for the next four weeks is shown in on the top left panel with the corresponding probabilities in the four panels of the bottom row. This forecast is based on a model of a fixed force of infection.  Onset is predicted based on a NULL model which uses historic values whereas peak week and intensity are selected from a force of infection model that depends on school vacation (and specific humidity) with the resulting typical double peak prediction for peak week: early (EW 52) or late (EW 6).

nation-EW45

Region 4 is the largest HHS region and its %ILI has just crossed the CDC onset value (dashed horizontal line in top left panel).  In agreement with this observation, our selected forecast predicts an early onset and an early peak week (EW 52).  The %ILI profiles shown in the top left panel are typical for our coupled S-I-R models with a time-dependent (school vacation and specific humidity) force of infection.

region4-EW45

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