Prognostic Importance of SARS-CoV-2 Plasma Nucleocapsid Antigen Levels

Treatment of COVID-19 includes antivirals or antibody products early on, with immunomodulators for select hospitalized patients during the subsequent inflammatory phase of disease. In a cross-sectional study, researchers evaluated the use of quantitative SARS-CoV-2 nucleocapsid (N) antigen levels as a marker of ongoing viral replication and hypothesize that an individualized approach to antiviral treatment in hospitalized patients is feasible.

A total of 2540 hospitalized patients who were enrolled in a trial of COVID-19 therapeutics underwent baseline viral N antigen measurement. Subjects were a median 8 days from symptom onset; 11% were fully vaccinated, 44% were infected with the Delta variant (enrollment was completed prior to the Omicron wave), and 95% had detectable N antigen. Participants were stratified by N antigen (<1000 ng/L or ≥1000 ng/L). Those with higher baseline levels had more-severe disease at enrollment. Other characteristics associated with higher N antigen levels included male sex, shorter time since hospital admission, and infection with Delta. Use of remdesivir prior to enrollment and vaccination were associated with lower levels. Higher N antigen levels predicted worse outcomes (odds ratio, 5.06 for worsening pulmonary status at day 5). Further, 26% of subjects on room air at enrollment who had higher N antigen levels required oxygen at day 5 versus 6% who had lower antigen levels.