Vagus nerve stimulation has also been used to treat some forms of epilepsy since the late 90s, and is being researched as a treatment for a wide variety of other illnesses and conditions: https://en.wikipedia.org/wiki/Vagus_nerve_stimulation
It's important to remember that this was never a first-choice treatment for seizures. VNS was only viewed as a worthwhile course to pursue after trying an exhaustive list of drugs.
From an FDA hearing on VNS: "there were patients who were very good responders, becoming essentially seizure-free, as well as patients who were poor responders, having 100 percent or greater increase in their seizure frequency," and it was very difficult to predict how a given patient would respond. [1]
