The verification comes from the data collected fro

The verification comes from the data collected from public sources. It is known that these people had Covid-19 and whether they had been vaccinated or not. There is no placebo effect when you have the simple determinatives of has Covid-19 when tests prove it or vaccinated/non-vaccinated when that is known. The objectivity is the data itself. There is no conclusion that needs to be inferenced since the data itself is self evident.