Edit: I see that this study did begin with the desired end in mind because they have a blurb titled "What are the implications for public health practice?" that says:
> All eligible persons should be vaccinated against COVID-19 as soon as possible, including unvaccinated persons previously infected with SARS-CoV-2.
In other words, these "scientists" decided to comment on public policy in their study. Such an act makes it extremely suspect for several reasons, not least of which the scientists are making a political statement in what is supposed to be a scientific study.