This is the fourth week of the CDC Flu Challenge. Three of the regions: 1, 4 and 6 have crossed the onset value. Whereas five regions (1, 2, 4, 6, and 7) and the national are still well above their historic average %ILI values, four regions (3, 5, 9 and 10) are below their historic average %ILI values for this time of year. Region 8 is following the average %ILI curve closely. Given this split between above and below average our selected forecast for the national peak week (second from right panel in top row) comes from a coupled spatial model with a force of infection that depends on the school vacation schedule and consequently shows a probability for either an early (EW 52) or later (EW 6-7) season peak. Our forecast for onset (second from left panel in top row) is based on a combination of a historic NULL model and our coupled spatial model (with dependence on specific humidity). Our forecast for the next four weeks is shown in the top left panel with the corresponding probabilities in the four panels of the bottom row. This forecast is based on a model with a time-dependent (school vacation and specific humidity) force of infection.
Region 6 had a large increase in the previous week and has crossed its %ILI onset value (dashed grey horizontal line in top left panel). Our prediction for onset (second panel from left in top row) is therefore centered at the current epidemic week. As with the national case, our prediction for the timing of this region’s peak is split between an early (EW 52) and a late (EWs 6-7) week. Our forecast for the next four weeks (top left panel) is based on a data augmentation procedure that uses %ILI data from previous seasons to inform the prior distribution used in the MCMC procedure.