Reach and engagement in the ECAIL trial targeting socially disadvantaged families across the COVID-19 pandemic and cost-of-living crisis: A mixed-methods implementation study

Background: The ECAIL trial, launched in 2017, was designed to evaluate a multicomponent intervention for childhood obesity prevention among hard-to-reach families. At a maternity hospital in Lille, France, healthcare providers screened pregnant women experiencing social vulnerability, and dietitians delivered a home-based intervention until age 2. The COVID-19 pandemic led to a six-month suspension in 2020. This study compared eligibility and participation before the pandemic and after resumption, and examined how implementation and reach evolved across the pandemic and subsequent cost-of-living crisis. Methods: Using a convergent mixed-methods design, we analyzed 5,744 eligibility questionnaires distributed at the maternity ward and conducted a focus group with six dieticians delivering the intervention to triangulate quantitative implementation indicators with qualitative implementation data. Inclusion criteria included ≥1 indicator of social vulnerability (e.g., socioeconomic disadvantage, precarious housing, or social isolation). The focus group was recorded, transcribed, and analyzed thematically focusing on reach, acceptability, and adaptation. Results: Eligibility increased from 29.7% (n = 955) pre-pandemic to 33.6% (n = 849) after resumption, while the distribution of vulnerability criteria remained similar across periods: 78.3% received social/medical benefits; employment was not the main source of household income for 58.7%; 24.4% experienced financial hardship; 14.7% reported social isolation; 6.0% lived in precarious housing; and 19.0% had three or more vulnerabilities. Participation among eligible women remained stable (24.6%; n = 443). Qualitative findings indicated dietitians’ satisfaction and participants’ enthusiasm for the resumption of home visits, particularly in addressing social isolation. After resumption, the introduction of a pre-visit COVID-19 questionnaire was associated with fewer failed home visits. Integration of quantitative and qualitative findings indicated sustained, and in some cases strengthened, provider engagement despite pandemic-related strain on hospital services. Conclusions: This study suggests that a complex intervention can maintain reach and acceptability through adaptive implementation under major contextual disruptions. The rapid resumption of home-based services emerged as a promising implementation strategy for engaging and retaining socially disadvantaged families, highlighting the importance of flexible, context-sensitive approaches during social and economic crises. Trial registration: Clinicaltrials.gov NCT03003117; registration date: 21/12/2016; https://clinicaltrials.gov/study/NCT03003117.