Our World in Data has aggregated massive data sets related to COVID-19. The vaccination data subset is available in a GitHub repository in csv format. The Matrix Portal is using data from this repository.
Our complete COVID-19 dataset is a collection of the COVID-19 data maintained by Our World in Data. It is updated daily and includes data on confirmed cases, deaths, hospitalizations, and testing, as well as other variables of potential interest.
The Center for Disease offers a much more limited data set that includes information for each state and the country as a whole in JSON format. The MagTag has been updated to use the data directly from the CDC