The post-acute phase (PAP) after COVID-19 (four months or more after the acute phase of
COVID-19) can manifest with reduced function in multiple organ systems, with a particular
focus on the lungs, cardiovascular system, and kidneys. Collectively, these three
non-communicable diseases (NCDs) represent a significant burden for both the individual
and society as a whole. There is an urgent need to elucidate this connection and build a
more detailed understanding of the link between COVID-19's PAP and individual NCDs,
as well as to identify robust biomarkers that can assist in the early identification of
the development of these NCDs.

This study focuses on PAP and the associated risk factors in this later phase of the
disease, examining the relationship between PAP and the increased risk of specifically
lung, heart, and kidney complications in the Danish population. Additionally, data
(medical records, registry data, patient reported outcomes and blood samples) from a
cohort of former patients hospitalized with COVID-19, as well as a control group
hospitalized with other respiratory diseases, are investigated to determine the
prevalence and risk ratios in disease development more precisely.

The purpose of the study is to contribute to minimizing the risk of developing or
worsening NCDs in current and future COVID-19 patients, as well as contributing to our
understanding of chronic disease development at the population level. The study aims to
investigate the hypothesis that biomarkers can predict if SARS-CoV-2 infection leads to
increased and exacerbated non-communicable pulmonary, cardiovascular, and renal diseases.

Further, we address the unmet need to understand the molecular mechanisms responsible for
the link between post-acute effects of SARS-CoV-2 and complications in the pulmonary,
cardiovascular, and renal system. More specific we will investigate the molecular
mechanisms responsible for the aetiology and decline in organ function.

The population in the registry study is the entire population of Denmark. The population
in the clinical cohort consists of former patients who have been admitted to Hvidovre
Hospital with the diagnosis OBS COVID. Participants consent to the use of residual
material from their blood sample, taken during their hospitalization with the diagnosis
OBS-COVID in the period 2020-2022 (index blood sample). After obtaining consent, patients
come to Hvidovre Hospital, where a blood sample (follow-up blood sample) is taken, and an
online questionnaire is completed and stored in REDCap. Blood samples are analyzed and
compared with collected registry data and questionnaire data, after which the results are
reported in international peer-reviewed journals.