This visualization shows ILINet flu surveillance data, plotting weekly ILI totals across multiple years with each year color-coded for comparison. It aggregates ILITOTAL values by year, region, and week, using bar marks to display the data. The code uses the vega-lite-api library to construct the chart, with d3.csv loading the data from a Gist-hosted CSV, and vega-tooltip providing interactive hover details. The visualization applies a custom config for improved label and title readability.