... even if everyone has been vaccinated."
Listen carefully to the puppet that is Matt Hancock
Haven't watched the video, but doesn't it make sense to keep up the quarantine practices for a bit longer after the vaccines?
It's a worldwide outbreak that stands to mutate, and the vaccines are rushed.
We'll likely be okay and lockdowns in the future, not immediate future, will likely be unnecessary given mRNA vaccination which is a breakthrough a long with the fact that any mutation should in theory not deviate enough from the current virus that current vaccination will be wholly ineffective.
However, and I do not know this for sure, it may be reasonable to think from an evolutionary standpoint vaccinations may potentially drive the virus to take on more extreme mutations as such mutations will be the only ones that can multiply effectively.
In the end this should become a situation much like H1N1, heard immunity to mutations within a standard deviation of current virus and vaccines to prepare for more extreme versions that pop up.