Background:
Given the large mental health treatment gap in low- and middle- income countries (LMICs), harnessing the naturalistic processes of diffusion- the untargeted and unplanned spread of new practices across networks- and spillover- the phenomenon of beneficial effects among nonparticipants- could shed light on the wider benefits of evidence-based mental health interventions in LMICs, including Sierra Leone. This study explored potential diffusion and spillover effects of an evidence-based mental health intervention- the Youth Readiness Intervention (YRI)- among peers and cohabitating caregivers of Sierra Leonean youth (aged 18-30) who participated in the intervention.

Methods:
We recruited index participants who had completed the YRI delivered within entrepreneurship training (N=165) and control index participants (N=165). Index participants nominated three of their closest peers and one primary cohabitating caregiver. Nominated peers (N=879) and caregivers (N=284) were recruited and enrolled into this study. Sub-samples of caregivers, index participants and peers were selected to participate in 20 key informant interviews, 11 dyadic interviews, and two focus group discussions (N=16), respectively. Qualitative data was analyzed using grounded theory. Multivariate regression analysis compared YRI knowledge levels among YRI participants’ peers relative to control participants’ peers.

Results:
Qualitative analysis indicated that spillover effects occurred among caregivers, via improvements in sense of well-being, household dynamics, and caregiving burden. Qualitative analysis supported diffusion of several YRI components among peers, particularly progressive muscle relaxation and diaphragmatic breathing. Sharing occurred mostly via verbal explanation or demonstration with same-aged peers. Regression analysis indicated that YRI participants’ peers (β=0.02, p<.00) demonstrated significantly greater YRI knowledge compared to control participants’ peers.

Conclusion:
Diffusion and spillover of evidence-based interventions can occur naturally in a post-conflict, LMIC setting. Disseminating evidence highlighting the wider societal benefits of evidence-based mental health interventions to key stakeholders and policy-makers in LMICs could help increase investments in scaling up services.