Participants were invited via letter including a personal access code; individuals that agreed to take part in the study signed a written informed consent and used their personal code to access online registration for the study visit. In case of study-related questions or technical issues, a hotline service was available. Online questionnaires were available from January 18th to February 6th, 2021. For participants that encountered difficulties in filling out the online questionnaires, study staff were available during the study visit to assist them. Study visits took place in one center located in Lausanne between February 1st and February 6th 2021, during which a locally developed serological test was administered, a Luminex assay detecting anti-SARS-CoV-2 IgG and IgA antibodies [24 (link)]. In case participants were unable to attend the study visit on-site, a home visit was possible by means of four mobile study teams. All data were collected and managed using the Research Electronic Data Capture (REDCap) tools hosted at Unisanté. REDCap is a secure, web-based software platform designed to support data capture for research studies [25 (link)].
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