COVID-19(14) mental health(7) effect size(6) Trial(6) baseline(6) COVID-19 pandemic(6) behavioural(6) Controlled(6) Worry(6) participant(6) Treatment(6) Intervention(6) reductions in(6) Psychological intervention(6) pandemic(5) Measures(3) mean difference(3) Efficacy(3) Inclusion(3) assessment(3) indicated(3) were recorded(3) Digital therapy(3) HADS(3) outcome(3) Controlled trial(3) greater(3) depression.(3) arising(3) reduction(3)