Mobile intervention to promote correct hand hygiene at key times to prevent COVID-19 in the Swiss adult general population: study protocol of a multiphase optimisation strategy.

introductionBehaviour change is key to the public health measures that have been issued in many countries worldwide to contain COVID-19. Public health measures will only take preventive effect if people adhere to them. Interventions taking health psychology approaches may promote adherence to public health measures. However, evidence from randomised controlled behaviour change trials is scarce during an ongoing pandemic. We aim to use the example of hand washing with soap to optimise and test a digital, theory-based and evidence-based behaviour change intervention to prevent the spread of COVID-19. METHODS AND ANALYSIS: This protocol describes the multiphase optimisation strategy for the preparation, optimisation and evaluation of a theory-based and evidence-based intervention delivered via app. The app aims to promote correct hand hygiene at key times in the adult general population. The study will be conducted in German-speaking Switzerland. The preparation phase has identified relevant behavioural determinants of hand hygiene during a pandemic from health behaviour theories and formative research with focus groups (n=8). The optimisation phase will identify the most effective and acceptable combination and sequence of three intervention modules in a parallel randomised trial (n=387) with analysis of variance (ANOVA) and regression analysis. Additionally, thematic analysis of qualitative interview data (n=15) will be used to gain insights on the feasibility, usability and satisfaction of the intervention. The evaluation phase will test the optimised intervention against an active control group in a randomised controlled trial (n=205), analysing pre-post differences and 6-month follow-up effects with ANOVA and regression analysis. ETHICS AND DISSEMINATION: The trial was approved by the Cantonal Ethics Commission Bern of the Swiss Association of Research Ethics Committees (protocol ID: 2021-00164). Final results will be presented in peer-reviewed journals and at conferences. TRIAL REGISTRATION NUMBER: NCT04830761.