Implications of the COVID-19 trajectory for the evaluation of hand hygiene interventions: Secondary analysis of the Soapp trial.

Hand hygiene is an effective behavior for decreasing the transmission of infectious diseases, including Coronavirus disease (COVID-19). During the early stages of the COVID-19 pandemic, hand hygiene was in part related to how the pandemic evolved over time (pandemic trajectory), e.g., how many people were affected or the number of deaths. We argue that such associations can confound conclusions about the effectiveness of interventions aimed at promoting hand hygiene during a pandemic. To test this hypothesis, we estimated how indicators of the pandemic trajectory influenced the evaluation of a smartphone app developed to promote hand hygiene during COVID-19. Our analysis included 216 participants who used the app for 34 days between March and August 2021 and reported their hand hygiene behavior using an electronic diary. Information on the pandemic trajectory were extracted from the World Health Organization database. Results confirmed that hand hygiene behavior increased with the use of the app when accounting for most pandemic trajectory indicators. However, this effect disappeared when accounting specifically for the total number of cases and deaths since the beginning of the pandemic. These results underline the importance of considering the pandemic trajectory when evaluating the efficacy of behavior change interventions carried out during an ongoing pandemic.