How do you know how it works then?
https://www.nytimes.com/2020/12/08/health/covid-vaccine-mask.html
It sounds like they're pretty sure the vaccine will prevent people from getting sick. It does not sound like they're sure that it will prevent them from being asymptomatic spreaders. It's unsure enough that Faucci talked about it. And not just him.
Because this virus acts like a virus?
I say again. Name one that where vaccinated person can be an asymptomatic spreader.
If I had to guess, they are giving themselves cover to keep restrictions in place for all as more and more people get vaccinated.