ILI forecasts for 2017-2018-Epidemic Week 46

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.

Picture1

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.

Picture2

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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

ILI forecasts for 2017-2018 – Epidemic Week 44

We’re into the second week of the CDC Flu challenge. We’ve developed some new graphics to assess our forecasts. This week we’re showing our “histogram plots”. The two images below (PDF versions can be downloaded in the link below each image) show probabilities for (top) national and (bottom) Region 1 summaries of (1) onset; (2) peak week; (3) peak intensity; (4) 1-week forecast; (5) 2-week forecast; (6) 3-week forecast; and (7) 4-week forecast.

The first panel in each Figure shows the current data (up through Epidemic Week 44) in red, together with our forecast (dotted line) and some realizations to give a measure of the uncertainty in the current forecast. The details of the model variants used to make these forecasts will be explained in more detail in subsequent weeks.

SubHists_EW44-national

SubHists_EW44-national

SubHists_EW44-region-1

SubHists_EW44-region-1

The distributions are fairly wide at the moment, reflecting our uncertainty in many of the parameters. As the weeks go by, these will narrow.