A commercial immunoassay Elecsys® Anti-SARS-CoV-2 S for the in vitro quantitative determination of antibodies to the SARS-CoV-2 spike (S) protein receptor binding domain (RBD) in human serum and plasma is used. This assay detects pan-Ig antibody response (pan-Ig anti-S1-RBD) and allows for a quantitative assessment of the serological response of the participants.

Qualitative measurement of anti-Nucleocapsid (N) responses with Elecsys® Anti-SARS-CoV-2 N assay

SARS-CoV-2-binding antibody responses of the participants are assessed by analyzing the IgM, IgA and IgG responses to a wider range of SARS-CoV-2 proteins (S1, S2, RBD and N) using an in-house method (ABCORA). The ABCORA test allows a parallel assessment of IgG, IgM and IgA reactivity.

Number of participants with newly PCR-confirmed asymptomatic COVID-19 infection (identified by the presence of anti-SARS-CoV-2 nucleocapsid antibodies or Sars-Cov-2 PCR or rapid antigen test) and no related symptoms \[(i.e. fever or chills, cough, shortness of breath or difficulty breathing, fatigue, muscle or body aches, headache, new loss of taste or smell, sore throat, congestion or runny nose nausea or vomiting, and diarrhea\])

Number of participants with newly PCR-confirmed symptomatic COVID-19 infection with at least one of the following symptoms (i.e. fever or chills, cough, shortness of breath or difficulty breathing, fatigue, muscle or body aches, headache, new loss of taste or smell, sore throat, congestion or runny nose nausea or vomiting, and diarrhea

Number of participants with severe COVID-19 infection with respiratory failure, evidence of shock (as diagnosed by a treating physician), clinically significant acute renal, hepatic, or neurologic dysfunction; admission to an intensive care unit; or death

COVID-19 burden of diseases (BOD), a composite, will be scored as by using 0 for no COVID-19, 1 for non-severe COVID-19, and 2 for severe COVID-19.

Duration of RCT set up (i.e. time from deciding which interventions will be tested until the first patient is randomised).

Patient consent rate (i.e. proportion of patients giving informed consent out of approached eligible patients)

Proportion of missing data for all clinical outcomes from routinely collected cohort data and outcome data that is collected in the trial platform

SARS-CoV-2-specific antibodies (using a pan-IgG antibody assay against the receptor binding domain (RBD) against the nP and spike 1 subunits)

SARS-CoV-2-specific titers (using an in-house assay developed by the Institute of Medical Virology, University of Zurich which can detect multiple viral epitopes)

The proportion of patients with a positive antibody response to SARS-CoV-2 spike (S1) protein receptor binding domain in human serum or plasma assessed or plasma assessed in the observational second sub- protocol by the commercial immunoassay Elecsys Anti-SARS-CoV-2 S (Elecsys S) from Roche Diagnostics. An antibody response will be considered as positive using the threshold ≥ 100 units/ml, predicting a protective immune response.