Optimising indicated prevention for child anxiety and depression: A 12-month follow-up for cluster-randomised factorial 2 x 2 x 2 trial

Background: Early intervention can reduce the burden of internalising problems for children and adolescents, yet access remains limited. The field must ensure preventive interventions that are both durable and scalable. One promising approach is developing interventions that are less resource- intensive yet retain components that are active in the long-term, enabling both sustained effects and wider reach. Methods: Through a 2 x 2 x 2 cluster-randomised factorial trial (www.clinicaltrials.gov NCT04263558) aimed at optimising an indicated child-focused group-intervention for internalising problems, we assessed the 12-month post-intervention effects of three components: (i) intervention delivery format (16-session group-format versus a blended format integrating eight group sessions with eight automated web-based sessions), (ii) parental involvement (five parent group sessions versus a psychoeducational parent brochure), and (iii) a measurement feedback system (symptom development tracking on versus tracking off). Respondents were 564 school children (aged 8 to 12 years) with heightened anxiety or depression symptoms, and 554 parents. The primary outcomes were children´s symptoms of depression and anxiety (child- and parent-report). Results: We did not find superiority of a group format over a blended delivery format. Furthermore, there was no evidence that parental participation in five group sessions significantly enhanced child outcomes compared to parents receiving a psychoeducational brochure. Finally, no significant main effects were observed for adding a measurement feedback system to track child symptom development during the intervention. Conclusions: Several components or intervention aspects may optimise indicated interventions for child and adolescent internalising problems. Despite no component amplifying intervention effects, there is optimism in recognising that a simpler combination of components might produce interventions as promising as more resource-demanding ones. Trial registration:ClinicalTrials.gov identifier: NCT04263558.