Thanks for the comment. I have a feeling that the reason they zoomed in on two seven day windows might be the computational difficulty of accounting for the way that the vaccination percentage changes over time in each particular location. By limiting it to two consecutive 7-day periods, I suppose that they might have just used a single number for vaccination percentage.

If so, that would also mean that they're ignoring any changes in vaccination rate that may have happened inside that 14 day window.

I hadn't noticed before, but the authors also provide a dashboard with US data from April through October. I don't see an easy way to get a multi-month summary of the data, though.