Study Questionnaires

Participants could complete the full online survey (extended survey) or, alternatively, a mandatory version (minimal survey). The minimal survey included basic epidemiological and clinical data required for the prevalence study on SARS-CoV-2 infections and immunity. The extended survey was based on the International Severe Acute Respiratory and emerging Infection Consortium (ISARIC) [11]. covering wide range of domains, including socio-economic factors and psychological wellbeing (Table ​(Table1).1). Minimizing potential language bias, all questionnaires were provided in four languages (English, French, Portuguese, and German). Supplementary Table 1 provides detailed information captured in the online survey.

The psychological test battery included: Center for Epidemiologic Studies Depression Scale (CES-D Scale), a 20-item measure assessing depressive symptoms (total range: 0—60) [12, 13]. Generalised Anxiety Disorder 7-item scale (GAD-7)—screening tool for anxiety (total range: 0—21) [14, 15]. University of California Los Angeles (UCLA) Loneliness Scale short version, a 3-item measure assessing the extend a person feels disconnected from others (total range: 3—9) [16, 17]. Perceived Stress Scale 4 (PSS-4), 4 item version of the classic stress assessment instrument (total range: 0—16) [18, 19]. Brief Resilience Scale (BRS) used to assess the perceived resilience scored on a Likert-Scale (total range: 1—5) [20]; Big Five Inventory 10 (BFI-10), a 10-item scale measuring the personality traits: Extraversion, Agreeableness, Conscientiousness, Neuroticism, and Openness (range: 1—5 for each) [21].

Health status evaluation focused on 29 symptoms associated with SARS-CoV-2 (summarised in Supplementary Table 2) and comorbidities.