Biden has no influence over the people who are still listening to Trump.
can confirm
i'd say that biden has tremendous influence over trump's acolytes: whatever biden says, trumpers will instinctively do the opposite. hence the current low vax rates among them, they're "sticking it to joe".
since biden has just about maxed out the number of vaccinations he can get on the left, he should switch tact and start denigrating vaccines, telling everyone that they shouldn't get them, that's they're a waste... that might drive the trumptards to the get the shot.