Your so called "new" study is dated 15th January 2021
The study https://www.thelancet.com/journals/l...648-4/fulltext is actually dated October 29 2021, so mass vax was a thing. The story referring to the "new study" quotes some other links, one of which is from January 2021. Apologies, I didn't see that one get pasted across.
before mass vaccination had even become a thing.
What difference does mass vaccination make? The study referred to the difference in exposure to vaccinated or unvaccinated persons by vaccinated vs unvaccinated. In the study either all were vaccinated or all were not vaccinated. That was the point.