Depression is a common illness, affecting 17% of the population over the course of a lifetime. A third of depressions relapses and progresses to recurrence and resistance to treatments. Despite the optimization of antidepressant medical strategies, 20 to 40% of depressions do not respond to treatment. This is particularly worrying as 6% of non-responder patients will die by committing suicide. Depression has a major impact on quality of life, socio-professional functioning and healthcare consumption. Sometimes, TRD is part of a bipolar illness. In this case, the challenge is even bigger because antidepressants are no well tolerated, further reducing the therapeutic options in case of resistance, the severity and duration of the depressive episodes are the main factors explaining the deterioration of the quality of life and the increasing cost of cares for these patients. The standard treatment for TRD is electroconvulsive therapy (ECT), which results in a response in 60 to 70% of cases after a few weeks of treatment. However, the improvement is often transient and 40% of patients relapse within 6 months of the initial ECT session. Moreover, ECT is often not well tolerated. This therapeutic impasse therefore makes TRD a priority public health target to which it is urgent to provide a realistic medico-economical response. The literature suggests that Vagus Nerve Stimulation (VNS) has unique kinetics of efficacy in depression, particularly in preventing long-term recurrences, and therefore responding to the lack of effective maintenance treatment in TRD. In fact, the benefits of VNS gradually accumulate over 12-24 months, which makes it complementary to more incisive treatments like ECT. Finally, its efficacy-tolerance profile appears to be similar in uni and bipolar TRD, giving VNS a potentially unique place in the therapeutic arsenal in psychiatry. The DepVNS hypothesis is that VNS is a medico-economically efficient therapeutic option to overcome the therapeutic impasse in which patients suffering from uni and bipolar DR currently find themselves due to the frequency of relapses under treatment. The primary objective is to estimate, from a collective point of view, the incremental cost-utility ratio of VNS to treat patients suffering from RD.