The aims of this case-control, non-randomized study including patients with post-COVID-19 persisting symptoms are 1) to establish the large blood biobank, 2) to examine levels of circulating inflammatory biomarkers and different classes of non-coding RNAs (ncRNA), such as selected circRNAs and miRNAs, in plasma and serum samples collected from patients with post- COVID-19, 3) to test the levels of cfDNA in plasma and serum, 4) to define correlation between ncRNAs and cf-DNA with persistent clinical symptoms, and type of symptoms, and 5) to investigate diagnostic and prognostic performances of these circulating biomarkers.

Study design. This is a prospective registry including biobank.

Currently, several studies are ongoing to investigate different treatment modalities of post-COVID-19 symptoms, but there is a complete lack of investigations on biomarkers predicting type, duration or severity of post-COVID-19 symptoms. The aim of this study is to investigate circulatory biomarkers diagnostic or predictive for long/post-COVID-19 syndrome.

Study patients. Patients with at least 3 weeks after proven infection by SARS-CoV-2, reflected by at least one positive PCR-test in nose throat swabs, who visits at the Post-COVID-19 outpatient clinic of the Medical University of Vienna, will be consequently recruited into the presented registry. Additionally, 100 vaccinated patients with HFrEF and 100 healthy vaccinated volunteers will be recruited to serve as comparison groups.

Methods. Identity of the registry patients will be protected by pseudonymization. During the ambulatory visit, basic clinical examination, electrocardiogram, chest X-ray, routine laboratory tests will be performed. Additionally, venous blood will be collected for biobank.

Expected Outcome This registry will provide further insights regarding pathophysiology, risk stratification and treatment of complex post-COVID-19 symptoms. Specific therapies and search of prognostic factors will enable to select patients with high risk of persistence or worsening of their symptoms thereby improve patient care.

Inclusion Criteria:

For post-COVID patient group:

• Age≥18to90years
• Proven infection by SARS-CoV2, at least 3 weeks after recovery from the infection
• Signed informed consent For HFrEF patient group:

For vaccinated healthy volunteer control group:

• Full vaccination against SARS-CoV2 at least 3 weeks before inclusion in the study
• Signed informed consent

Exclusion Criteria:

• non-willingness to participate or withdrawal of informed consent
• Clinically confirmed HFrEF (EF <40%)
• participation in any SARS-CoV-2 medical treatment trial
• pregnancy

Outpatient clinical patients with at least 6 weeks after proven infection by SARS-CoV-2, reflected by at least one positive PCR-test in nose throat swabs, who visits at the Post-COVID-19 outpatient clinic of the Medical University of Vienna, will be consequently recruited into the presented study. A written informed consent will be present before inclusion. 100 vaccinated HFrEF patient volunteers will be recruited during routine visits to our outpatient clinic. 100 healthy, vaccinated volunteers will be recruited from among hospital staff.

upon reasonable request; after signature of the Data Sharing Agreement

After the study closure, and publication of the data

Upon reasonable request; after signature of the Data Sharing Agreement