Overall in this project, the primary goal is to evaluate the efficacy of virtual reality exposure (VRE) for adolescents with elevated social anxiety using a three-arm randomized controlled trial: (1) virtual reality exposure (VRE); (2) in vivo exposure (IVE); and (3) waitlist (WL) - the control condition.

It is predicted that both VRE and IVE will be more successful in decreasing social anxiety symptoms than the WL condition at post-assessment and that VRE will be as effective as in vivo in reducing social anxiety symptoms. Furthermore, it is expected that there will be no difference between the two active conditions in the long term (at 3- months & 6-months follow up). Similar results are expected in the secondary outcome measures, intended to capture the participants' general well-being.

Moreover, the study has the following (secondary) objectives:

• To elucidate potential working mechanisms of VRE and IVE
• To identify predictors of adolescents' response to VRE and IVE
• To assess to what extent adolescents accept VRE and IVE and how they experience it

This study is going to be a single-blinded, randomized controlled trial (RCT) with three arms: VRE, IVE, and a WL condition. It will follow a mixed-subjects design with condition as a between factor and measurement time-points as a within factor. Due to the study's goal to unravel the effects of VRE, the focus of the intervention will be on exposure in both active conditions (without explicitly including other treatment components like cognitive restructuring). The intervention will take place either at participants' schools or at KU Leuven (i.e., PraxisP - the outpatient treatment facility of the Faculty of Psychology and Educational Sciences, PSI - Psychological Institute) depending on the participants' preference and availability. In case this is not possible, neighboring healthcare practices will be explored as an alternative option. In any case, the training will be held in a separate, private room where the privacy of the participant can be guaranteed. Each active condition will comprise of 7 training sessions in total approximately 90 minutes each.

At pre-assessment, all primary and secondary outcome measures and most of the predictors will be assessed approximately one week prior to the first session. The outcome measures will be re-assessed during the post-assessment (one week after the last session) and the follow up assessments (3-months & 6-months following the post assessment). During the training sessions, measurements of the mechanisms, remaining predictors, and participant feedback will be acquired and at mid-assessment an additional measurement of the primary outcome measures (e.g., social anxiety measures) will be obtained. Moreover, a brief social anxiety measure will also be conducted on a weekly basis to record symptom-related changes from session to session. Following the training, a qualitative interview will be conducted. This semi-structured interview will be conducted in a convenience sample of participants from both active conditions (e.g., 10-16 participants per condition due to pragmatic considerations and based on general recommendations as to when theoretical data saturation can be reached) to investigate VRE's acceptability and to compare it to IVE. To decrease demand effects, the (online) interview will be conducted by an independent interviewer (e.g., not the therapist) and will be audio-taped so that the interviewer can focus solely on the interaction.

Moreover, in line with good clinical practice and individualized treatment, the specific nature and content of the exposure exercises will be determined for each participant individually by presenting them with an extensive list of the possible exercises (e.g., ordering food in a restaurant, asking a question in class, engaging in a group conversation) in combination with a functional analysis. To ensure that the active conditions are comparable, the IVE condition will be matched to the VRE condition in terms of exposure duration and homework assignments will not be actively encouraged in both conditions. The crucial difference between the two active conditions is that in the IVE condition the exercises take place in real life, whereas in VRE the exercises take place in virtual reality. For the WL condition, the (primary and secondary) outcome measures will be administered before, during, and after the given waiting period (i.e., duration of training sessions) at the same instances as with the active conditions. After that time, participants in the WL condition will have the opportunity to be randomized into IVE and VRE.

Inclusion:

• Elevated levels of social anxiety (as per the Social Phobia Inventory; ≥ 19)
• Fluent in Dutch
• 12-16 years old

Exclusion

• Severe social anxiety disorder
• Severe depression
• Psychotic symptoms
• Severe suicidal thoughts and / or severe self-harm
• Severe substance use
• Benzodiazepine use and / or a change of psychoactive medication usage (dose, type)
• Autism spectrum disorder (ASD) diagnosis
• Current ongoing psychological treatment (or waitlisted) for anxiety disorders and or depression
• Other urgent psychopathologies and/or mismatch between participants' clinical presentation and the offered training
• Exposure therapy for social anxiety disorder in the past 2 years
• Another person from the same household is participating in the study
• Eligible for VR as per the following criteria:
• History of extreme/severe motion sickness (e.g., car sick, sea-sick) and / or experiencing extreme/severe symptoms of motion sickness during 3D movies
• Stereoscopic vision problem or a balance problem that would hinder the VR experience;
• History of seizures, seizure disorder or epilepsy

There are no concrete plans to upload individual participant data on to any platforms. However, if other researchers request for the pseudo-anonymized data, then an agreement can be made to share the data.

All pre-assessments and post-assessment will be conducted by researchers who will be blind to the participants' allocated condition.