Introduction
Circulation of viral antigen in blood is a mainstay of diagnostic
testing in systemic viral infections, including HBV, HCV or HIV.
However, in respiratory infections such as SARS-CoV-2, antigenemia in
serum is harder to interpret [1,
2]. Systemic presence of nucleocapsid
(NCP) as well as spike (S) protein has been described
[3]. A high level of serum NCP antigen
was consistently found to be associated with serious illness
[4-7]. It was suggested that the serum
NCP antigen level may serve as an early biomarker for predicting the
maximum disease grade of severe COVID-19, using NCP antigenemia as a
tool for allocation of ICU options on admission
[8]. However, some patients progress
to more severe disease not before the second week of Covid-19; for those
patients, no biomarker has been established yet. Here, we demonstrate a
delay of NCP antigen clearance in patients who required intensive care
during hospitalization.