Advancing sustainable implementation of an evidence-based mental health intervention in Sierra Leone's schools: protocol for a hybrid type 3 implementation-effectiveness trial.

Background: Mental health disorders among youth contribute substantially to the global burden of disease, which is exacerbated in low- and middle-income countries (LMICs) due to large mental health treatment gaps. In Sierra Leone, a West African country with a long history of complex adversity, the mental health treatment gap is estimated at 98%. Implementing innovative mental health interventions that can be sustained at scale is a priority.