From the Document: "The sources [in this document] can help congressional staff track the progress of the U.S. COVID-19 [coronavirus disease 2019] vaccination campaign at the national, state, and local levels. Sources were selected for having commonly cited and frequently requested data. This list is not intended to be comprehensive. Additional sources may be added in future updates. Because different resources use different methodologies, readers should check websites' notes, definitions, and caveats. Readers should also use caution when comparing data across sources or geographies."
CRS Insight, IN11595
Congressional Research Service: https://crsreports.congress.gov/