This full factorial trial is part of the RECONNECTED project (www.reconnected-project.eu). RECONNECTED involves a consortium of 11 European partners responding to global societal developments affecting mental wellbeing of vulnerable citizens. The project will offer a digital support system with culturally adapted and personalised intervention tools to various vulnerable populations that are understudied and difficult to reach with regular mental health interventions (i.e. youth, people with low SES, migrant populations, and older adults). The digital support system targets both individual and social factors simultaneously (i.e. mental health literacy, psychological resilience and social connectedness) to maximise health benefits. The main aim of this trial is to examine if personalised micro-interventions and social activation add wellbeing benefits to mental health literacy. The additional effects of personalised micro-interventions and social activation to mental health literacy will be tested through nine full factorial trials in nine European countries. The second objective is to evaluate whether integrating a machine learning algorithm into personalised micro-interventions improves the effectiveness of the personalised micro-interventions compared to the standard version. This analysis will be conducted using pooled data from the nine trial sites. The third objective is to conduct a process evaluation to assess the feasibility of the digital support system, including usability, perceived usefulness, overall satisfaction, potential unintended negative effects, and engagement.

Europe is experiencing a period of rapid transformation, driven by digitalisation, changing demographics due to urbanisation, ageing, and migration, as well as global developments such as climate change and geopolitical instability (European Commission, 2023). While developments bring new opportunities, such as greater global connectivity and increased flexibility in work and education, they also introduce cognitive and emotional challenges. These challenges include, amongst others, identity struggles, shaped by factors such as migration and social media, and information overload and social disconnection due to urbanisation and digitalisation. Research has shown that not all citizens adapt equally well to these changes. It is suggested that vulnerable citizens in Europe, such as people with low socioeconomic status, immigrants, youth, and elderly, are affected the most by global societal developments. Hence, putting vulnerable citizens at higher risk for lower mental wellbeing.

Increasing mental wellbeing in vulnerable citizens:

Psychosocial interventions are a viable way to empower individuals to gain more control over their life, learn how to adapt to stressful events and promote mental health and wellbeing (World Health Organization, 2021). They often extend beyond a sole focus on individual behaviours, incorporating a broader range of social and environmental interventions (World Health Organization, 2021). This multilevel perspective aligns with the RECONNECTED project that adopts a complex system perspective on mental health and wellbeing that takes into account risk and protective factors at different levels of description: societal challenges (meta), living environment (macro), social factors (meso), and individual factors (micro) . To maximise mental health benefits, it is suggested that interventions need to address various risk and protective factors across multiple levels (e.g., meso and micro). In the RECONNECTED project, we offer a digital psychosocial intervention with culturally adapted and personalised intervention tools to various vulnerable populations in Europe. This is a multicomponent intervention that targets mental health literacy, social connectedness, and psychological resilience.

et pour la description : Europe is experiencing a period of rapid transformation, driven by digitalisation, changing demographics due to urbanisation, ageing, and migration, as well as global developments such as climate change and geopolitical instability (European Commission, 2023). While developments bring new opportunities, such as greater global connectivity and increased flexibility in work and education, they also introduce cognitive and emotional challenges (Molua, 2024; Romanello et al., 2021). These challenges include, amongst others, identity struggles, shaped by factors such as migration and social media, and information overload and social disconnection due to urbanisation and digitalisation (Saiphoo & Vahedi, 2019). Research has shown that not all citizens adapt equally well to these changes. It is suggested that vulnerable citizens in Europe, such as people with low socioeconomic status, immigrants, youth, and elderly, are affected the most by global societal developments (Benevolenza & DeRigne, 2019; Molua, 2024; Vasilescu et al., 2020). Hence, putting vulnerable citizens at higher risk for lower mental wellbeing (Benevolenza & DeRigne, 2019; Molua, 2024; Vasilescu et al., 2020).

Increasing mental wellbeing in vulnerable citizens Psychosocial interventions are a viable way to empower individuals to gain more control over their life, learn how to adapt to stressful events and promote mental health and wellbeing (World Health Organization, 2021). They often extend beyond a sole focus on individual behaviours, incorporating a broader range of social and environmental interventions (World Health Organization, 2021). This multilevel perspective aligns with the RECONNECTED project that adopts a complex system perspective (Mitchell, 2009) on mental health and wellbeing that takes into account risk and protective factors at different levels of description: societal challenges (meta), living environment (macro), social factors (meso), and individual factors (micro). To maximise mental health benefits, it is suggested that interventions need to address various risk and protective factors across multiple levels (e.g., meso and micro). In the RECONNECTED project, we offer a digital psychosocial intervention with culturally adapted and personalised intervention tools to various vulnerable populations in Europe. This is a multicomponent intervention that targets mental health literacy, social connectedness, and psychological resilience.

Mental health literacy is a core component of most psychosocial interventions. It aims to increase knowledge and understanding about mental health and illness and how to get support if needed (Jorm, 2015; Jorm et al., 1997) and has demonstrated the ability to increase mental health awareness, reduce stigma, and change attitudes towards mental health and mental health seeking behaviours (Brijnath et al., 2016). Research has shown that vulnerable populations, such as individuals with lower income and educational levels, tend to have lower mental health literacy compared to those with higher socioeconomic status (Soria-Martínez et al., 2024), which is important considering that low mental health literacy is one of the primary reasons for the treatment gap between those who need help and those who seek help (Tambling et al., 2023).

Social connection, social support, and a sense of belonging are fundamental human needs (Baumeister & Leary, 1995; Wickramaratne et al., 2022). Strong social networks foster belonging and act as protective factors for mental well-being by providing support and resources, enhancing self-worth, and broadening perspectives (Keim-Klärner et al., 2023; Steinhoff & Reiner, 2024). Social isolation, on the other hand, is associated with increased risks of anxiety, depression, and other psychological distress (Baumeister et al., 2007; Rutenfrans-Stupar et al., 2019; Wickramaratne et al., 2022). Therefore, social connectedness is particularly crucial for overall wellbeing (Rutenfrans-Stupar et al., 2019) especially when people experience high level of stress and uncertainty.

Resilience is commonly defined as the capacity to adapt to and recover from adversity. A theoretical approach to understand resilience, is the 'metatheory of resilience and resiliency' (MRR) (Richardson, 2002), which aligns well with the RECONNECTED conceptual framework. MRR emphasizes the dynamic interaction between individuals and their environment in managing and recovering from adverse life events. Resilience is thus not simply an individual trait (micro) but is influenced by external factors, such as social support (meso) and access to resources (macro) (Hall et al., 2023; Liu et al., 2017; Patel et al., 2017). Being a vulnerable citizen has been found to be associated with decreased resilience, making them more susceptible to the negative effects of adversities (Siriwardhana et al., 2014). By fostering resilience, individuals can develop greater emotional adaptability and coping mechanisms to navigate stressors more effectively (Siriwardhana et al., 2014). One way to enhance resilience could be through micro-interventions. Micro-interventions target specific social and psychological processes and alter the way that people think, feel, or behave in their daily lives (Fuller-Tyszkiewicz et al., 2019). Micro-interventions conceptually differ from standard and brief interventions in their scope, objectives, and time frame (Baumel et al., 2020; Elefant et al., 2017). They are narrower in focus, with a clear and targeted goal, and a timely approach, reducing the effort needed for completion. Unlike traditional interventions that often target broad clinical outcomes (e.g., reducing social anxiety), micro-interventions are designed to address more immediate and situational challenges, such as reducing stress before an exam or overcoming hesitation to attend a social event (Baumel et al., 2020). While their initial focus is to generate short-term positive effects, they contribute incrementally to longer-term goals like enhancing overall well-being (Fuller-Tyszkiewicz et al., 2019). In addition, micro-interventions offer greater scalability by being low-cost and overcoming common barriers to access, such as time constraints and scheduling difficulties (Lee et al., 2025).

Digital solutions:

Existing interventions psychosocial interventions do not always reach those in need due to limited cultural adaptation, language barriers, as well as lack of personalisation. These challenges are further reinforced by stigma, low mental health literacy and the high costs of interventions, which particularly affect socially disadvantaged groups (Dobalian & Rivers, 2008; Jorm, 2012). Digital interventions present a promising solution to bridge this gap by empowering individuals' self-management and enhancing scalability, affordability, accessibility, and safety of interventions (Aschentrup et al., 2024; Muñoz, 2010; Stark et al., 2022). Furthermore, empirical evidence supports the efficacy, effectiveness, and acceptability of digital health promotion and prevention tools (Muñoz, 2010). Moreover, evidence has shown that mental health literacy interventions, social activation, and micro-interventions can also be delivered digitally effectively. For instance, a meta-analysis of digital mental health literacy interventions reported large effect sizes for improving literacy and medium effect sizes for mental health outcomes, comparable to face-to-face interventions (Yeo et al., 2024). Similarly, digital interventions focusing on increasing social connectedness offer enhanced usability by enabling on-demand access and consolidating activity information in one platform, making it more user-friendly than traditional pen-and-paper methods (Lee et al., 2023; Patel et al., 2021). Moreover, digital delivery of micro-interventions provides unique advantages, such as automatic monitoring, notifications, and integrated messaging tools, which are not feasible in offline formats (Baumel et al., 2020) To realize the potential of digital interventions, they need to be tailored to the specific needs and cultural context of the target population. Cultural adaptation means alignment of interventions with the cultural context of the target population. This may include language adjustments and the use of culturally meaningful metaphors, such as symbols and sayings (Bernal et al., 1995; Nagayama et al., 2016). Personalisation, on the other hand, means adjustment of intervention with the individual's (current) needs and characteristics. This means that, based on these factors, a specific intervention may or may not be offered (Cohen et al., 2021). Persuasive technologies, such as machine learning algorithms, can support personalization by predicting an individual's psychological state and informing decisions about whether, when, and which intervention to offer (Abd-Alrazaq et al., 2023; Baumel et al., 2020; Ciharova et al., 2024; Moshe et al., 2021).

Inclusion Criteria:

• Mental well-being status: Classified on the MHC-SF as either "Languishing" or "Moderately Mentally Healthy."
• Age: Must be 18 years of age or older.
• Location: Resident of disadvantaged areas within the Val-de-Marne department, defined for this study as municipalities with the highest percentage of households living below the poverty line (more than 20% of households, according to INSEE data).
• Skills: Must demonstrate a sufficient level of linguistic and cognitive understanding to communicate with the research team and complete the pre-screening process.
• Resources: Must have access to a smartphone with an internet connection for the duration of participation in the study.

Exclusion Criteria:

• Severe mental illness: Self-report screen: "Do you currently have any of the following mental disorders diagnosed by a psychologist, psychiatrist, or other mental health professional?" (checklist includes schizophrenia, bipolar, psychosis, severe depression with hospitalisation).
• Mental Health treatment: Self-report screen:

"Do you currently receive psychological treatment for a mental disorder?" "Have you started taking prescribed medication for psychological or psychiatric problems (e.g., anxiety, depression, sleep problems) within the past four weeks?" (yes/no)

• Inability to commit to engagement: Self-report screen: "Are you able and willing to use the digital tool weekly for the next 6 weeks and complete 4 surveys?"
• Insufficient language comprehension: Basic comprehension check. Part of (electronic or in-person) consent procedure: prospect can read and understand the study information.

Resident of disadvantaged areas within the Val-de-Marne department, defined for this study as municipalities with the highest percentage of households living below the poverty line (more than 20% of households, according to INSEE data).