Very interesting exploration! btw, there is a WFR item for retrieving OWID data, too: https://resources.wolframcloud.com/FunctionRepository/resources/OWIDCOVID19Data/
Thanks for your reply.
I didn't know that vaccination data is available in Wolfram repository. Good to know ;)
The csv data file I used is referenced by https://ourworldindata.org/covid-vaccinations .
The notebook link https://www.wolframcloud.com/env/damcalrom/Published/Vaccination_Analysis.nb