Leveraging Influencers to Reach and Engage Vulnerable Individuals: A Quasi-Experimental Field Study with a Digital Health Intervention (Preprint)

Background: Non-communicable diseases (NCDs) are the leading cause of death, present economic challenges to healthcare systems worldwide, and disproportionally affect vulnerable individuals of low socioeconomic status (SES). While digital health interventions (DHIs) offer scalable and cost-effective solutions to promote health literacy and encourage behavior change, key challenges concern how to effectively (a) REACH and (b) ENGAGE vulnerable individuals. To this end, (a) social media influencers provide a unique opportunity to reach millions; and (b), ensure lasting engagement by designing DHIs in a manner that specifically appeals to low SES individuals through alignment with their social background. Objective: The objectives of this study are twofold: To assess the effectiveness of leveraging influencers to reach vulnerable individuals (as measured via app downloads per stream viewers) and to evaluate how the design of a DHI can improve engagement among this group (as measured via completion of intervention). Methods: This study utilized a cross-sectional, quasi-experimental field design to assess both (a) the effectiveness of influencers reaching vulnerable individuals and (b) the impact of specific design elements—such as gamification and storytelling—on user engagement with a stress-management DHI featuring a slow-paced breathing exercise. Three differently designed versions of this DHI were developed following a fractional factorial design (i.e., STRESSLESS, BREEZE, and TRAGICKINGDOM). Reach was calculated as the number of downloads per viewers per stream and influencer. Engagement with the DHI was measured via number of conversational turns, and milestone and intervention completion rates. Participants' SES and technology acceptance were evaluated through a post-intervention survey. Descriptive statistics, ꭓ2-tests, and ANOVAs were used to examine effects of the DHI design on reach and engagement metrics. Results: The recruitment via eight influencers (Total Streams = 25; Total Viewers = 12,667) generated 220 downloads. The average reach ratio across streams amounted to 16.2%, with significant differences between conditions, ꭓ2(2) = 8.04, p = .018: STRESSLESS: 8.1%; BREEZE: 14.0%; TRAGICKINGDOM: 28.4%. The intervention completion rate across all DHI versions amounted to 7.7% (17 out of 220), with no significant differences between conditions. Conclusions: This work provides first evidence that recruitment via influencers yields high reach ratios, moving far beyond the reach of traditional social media platforms. Nonetheless, based on the data collected, the ability to leverage such platforms to recruit and engage vulnerable individuals with DHIs remains unclear. Additionally, while engagement with the promoted interventions was initially high, completion rate of the full breathing exercise was comparably low, indicating that influencer promotion strategy cannot fully overcome the well-documented adherence barriers in digital health.