One thing to consider is that vaccine production is going to scale up in time; since the second dose is a month after the first, giving two doses instead of one will not mean that half the number of people will be vaccinated. Assuming, for the sake of the argument, that vaccine production doubles every month, at any given point after the first month the amount of people that have received at least one does will be a bout 2/3rds of the single dose protocol.