To properly test the efficacy of vaccine, you need a large group of subjects, half of which get the vaccine and half of which get an inert injection.

The trial has to be blind with neither participants nor scientists knowing who got vaccine and who got the inert substance.

Then, to test efficacy, you need exposure of both groups to infection to verify that those who got the vaccine were protected and to verify that those who didn’t developed the disease. The source of infection has to be proved viable as well as the vaccine.

For safety, you need long term studies in every age group which will receive the vaccine, and for live virus vaccines you need safety studies in all species which might be exposed to virus via shedding From the vaccinated subjects.

You cannot do all that in 6 months. Vaccinating entire populations with an untested vaccine would constitute criminal negligence and a possible crime against humanity,