JMIR Publications

ABSTRACT

Background:

Background:

Frontline workers are essential workers who keep the public safe, deliver care, and sustain the services on which society depends. Their work brings repeated exposure to trauma and chronic stress, making resilience building and timely support a workforce priority. Yet stigma, confidentiality concerns, and workload patterns and pressures deter help-seeking, and most digital mental health tools are generic rather than trauma-informed or occupationally tailored. Sentinel is a co-created, trauma-informed, self-guided digital intervention developed with frontline workers to build resilience and offer early support.

Objective:

We aimed to evaluate changes in mental health, well-being, burnout, and psychological safety outcomes following 6 weeks of access to Sentinel; to characterize acceptability and engagement; and to explore frontline workers’ experiences of using the intervention.

Methods:

In this 6-week single-arm convergent mixed methods study across multiple UK frontline sectors, participants, recruited from August 2025 to July 2026, completed pre- and postintervention measures of posttraumatic stress, depression, anxiety, stress, mental well-being, burnout, work engagement, psychological safety, quality of life, and posttraumatic growth. Acceptability and engagement were assessed using the User Version of the Mobile Application Rating Scale (uMARS) and participant-reported frequency of use. Semistructured interviews were analyzed using reflexive thematic analysis, and findings were brought together in an integrated results matrix.

Results:

Of 1178 individuals who accessed the survey, 438 (37.2%) provided baseline data and were enrolled; 109 (24.9%) completed a matched postintervention assessment, and 15 were interviewed. Participants were most commonly transportation workers (148/392, 37.8%) and paramedics or ambulance staff (71/392, 18.1%). In exploratory, unadjusted analyses of matched completers, improvements occurred on 11 of 14 outcomes, including posttraumatic stress symptoms (Cohen d=−0.31; P=.002), depression (d=−0.47; P<.001), stress (d=−0.40; P<.001), anxiety (d=−0.22; P=.02), burnout (d=−0.38; P<.001), mental well-being (d=0.42; P<.001), psychological safety (d=0.29; P=.003), and health satisfaction (d=0.39; P<.001). Work engagement, posttraumatic growth, and the psychological safety compassion subscale showed no statistically significant change. App quality was rated favorably (uMARS mean 4.03/5, SD 0.64), and 72 of 112 respondents (64.3%) used the app at least weekly. Six themes described in-the-moment support, reduced fear of judgment, accessibility, emotional validation, cultural barriers to engagement, and the importance of organizational endorsement.

Conclusions:

Among matched completers, posttraumatic stress, depression, anxiety, stress, burnout, well-being, and psychological safety improved over 6 weeks of access to Sentinel, with small-to-medium effects, alongside favorable acceptability and regular engagement among most respondents. Qualitative findings suggest that private, occupationally relevant, in-the-moment support may help workers attend to their mental health where acknowledging distress carries professional risk. Given the single-arm design and substantial attrition, changes cannot be attributed solely to the intervention. These findings justify a prospectively registered randomized controlled trial of Sentinel as an early intervention and prevention tool within organizational mental health pathways. Clinical Trial: International Registered Report Identifier (IRRID): RR2-10.2196/72250