Clinical, Virological, Serological and Immunological Characteristics During and Following COVID-19 Hospitalization: a Prospective Cohort Study

The studys primary aim is to assess clinical factors, such as disease severity, associated with neutralizing antibody (NAb) production. Furthermore, the study aims to assess the length of SARS-CoV-2 infectiousness and clinical factors associated with viral load.

Patients 18 years or older hospitalized at Copenhagen University Hospital at North Zealand, Copenhagen, Denmark, May 24th,2020 - May 5th, 2021, were routinely screened for COVID-19 by diagnostic oropharyngeal or tracheal RT-PCR samples taken during admission. Patients with a positive SARS-CoV-2 PCR within 48 hours from hospital admission were offered inclusion, if COVID-19 pneumonia was confirmed.

The following were retrieved from patients' electronic records: comorbidities (Charlson Comorbidity Index),vital signs (Early Warning Score), immunocompromised status, time from symptom onset to admission, oxygen treatment, pharmacological treatment, admission length, death and bacterial co-infection.

Paired oropharyngeal swabs and serum samples were collected at inclusion (day 0), days 3, 7, 10, 14, 17, 24, and 30. Serum samples were, if possible, also collected after three and six months. Follow-up time was six months.

RT-qPCR analysis targeted the SARS-CoV-2 RNA-dependent-RNA-polymerase (RdRp)-helicase gene region and two samples with known viral load were included in each PCR-run for quantification of patient samples. Virus was cultured in African green monkey cells (VERO-E6) with incubation for 3 - 4 days and daily microscopic inspection for cytopathogenic effect (CPE). A total of three passages were made before the the virus was interpreted as non-replicant. Cells with CPE were confirmed by RT-qPCR.