How do you beat Soraka/Vayne?

you probably won't kill Vayne until Soraka dies or if you can outburst Soraka's sustain. Instead of an Engage like Leona, I'd probably recommend a reverse engager like blitzcrank to separate them

How to make Soraka useless:

1. Have your mid rush Morellonomicon
2. Trollface.jpg
3. Profit.

How to make Vayne useless:

1. Ban that pain in the ass. It feels good.

The ideal thing is to catch Soraka out of place, or to just full on burst murder her before she can heal anyone.

I enjoy taking champion such as Talon against Soraka, He can jump straight into their backline and butcher Soraka before she has a chance to ult.

Varus is a great champion against a Soraka because of the Grievous wounds on his Hail of Arrows.

Additionally Morellonomicon is a fantastic item for your mid laner to take into the game because of it's Grievous wounds passive as well.

The problems with Vayne in general is that she goes super hyper carry, the only real way to shut her down in late game is to focus her first, keep her down all game long (As in not letting her farm up either.), or to CC lock her up. The biggest problem with a Vayne Soraka team is that you need to kill Soraka, so she doesn't constantly heal Vayne over and over again, so you almost have to split focus, which is very difficult to do and not throw the teamfight. I suppose something that could work, is blow a lot of CC on Vayne, while focusing the Soraka and killing her off, but that takes a lot of coordination with your team.

Kill soraka.

You don't You need to kill first in order to be able to kill , who you need to kill ASAP in order to not die.