Swain doesn't counter him. He might counter a bad Vladimir player, but once Vlad buys specters cowl, Swain has 0 kill potential. The logics the same with executioners calling. It doesn't counter Vladimir, and you're paying 800g for a long sword.
For the most part, once Vlad has WotA + Ionian + Defensive item, he wins most 1v1's on equal ground. You have to devote 2+ people to him, same way you would a Nasus or Darius. If you're trying to 1v1 at that point, avoid fighting in minion waves. In team fights, Vladimirs going to try to stay in the middle and AOE. Don't let him get off a multi-target ult, try to focus him down whenever possible.
Counters, Morgana and Fiddlesticks late game. Vladimir loses lane to most top laners early. Just have to consistently all-in him whenever possible.