Countertransference is ongoing and part of the therapy to. It's minimized when a therapist worked through their own transferrences in their own therapy.

The key is for them to be aware of it, to manage it, and to keep it from affecting the work as much as possible. Also to use those feelings to learn about the client.

Not being aware of it and managing it can be very destructive, which is one reason I won't see a therapist who hasn't worked through their own transference.

It's not unavoidable to have the countertransference, it's what they do with it that's critical.