After a little googling I also found an additional source for normalized time series provided by DataHub.io relying on the very same data.
However what I did not find was an OData v4 based service for retrieving any COVID-19 related data which might be helpful for others because this is their preferred way for consuming data, e.g. in a business context.
As the data provided by JHU CSSE and DataHub.io is mainly distributed via .csv files the solution was pretty simply:
Download the latest csv files from DataHub.io
Deploy these csv files as initial data to a @sap/cds based OData v4 service