> It does look like there's about a 20-30% reduction of infection from random surveys of the population and from nucleocapsid seroprevalence assays; transmission-once-infected is very difficult to measure, but it would be surprising if it did not have some effect.

You are responding to a practical concern with a theoretical counter. But practically speaking the vaccine doesn't change the picture at all. The situation pre-vaccine was COVID was going to spread like wildfire after any lockdown attempt ended and everyone was going to be exposed to it. The situation post-vaccine, even with that reduction in infection rates, was the same.

Ditto speed, since this is an exponential process that reduction won't have an especially material effect on when everyone gets COVID.

We ran a natural experiment on this in Australia [0] - having a highly vaccinated population didn't appear to have any impact at all on COVID transmission rate or reach in who gets infected. The numbers are not convincing that the vaccine did anything for transmissions. The effect of personal protection seems to explain all the benefits of the vaccine.

[0] https://chrisbillington.net/COVID_NSW.html