This fork of a line chart example uses d3.v5 to visualize vaccination data over time, with a vertical line marking a selected year. Users can hover over the chart to update the selected year via a mouse interceptor that inverts the x-scale, and a d3.ordinal color scale distinguishes regions. The visualization is rendered with SVG, axes, and line paths using d3.line and curveBasis, with data processed from CSV files.