UK's ONS report: "COVID-19 vaccine effectiveness estimated using Census 2021 variables, England: 31 March 2021 to 20 March 2022"; look at how vaccinated versus unvaccinated status was defined

by Paul Alexander

'The vaccination statuses used were: unvaccinated (those with no vaccination or who were vaccinated with a first dose less than 21 days ago)'; so tell me, what is wrong with that definition?