Baseline Plasma Viral Antigen Levels Are Associated with Clinical Deterioration in Hospitalized Covid-19: Potential Value for Stratifying Patients for Therapeutic Interventions

ABSTRACT

RATIONALE Some biomarkers of host response to viral infection are associated with COVID-19 outcomes, but these biomarkers do not directly measure viral burden. The association between plasma viral antigen levels and clinical outcomes has not been previously studied. Our aim was to investigate the relationship between plasma SARS-CoV-2 viral antigen concentration and proximal clinical deterioration in hospitalized patients. METHODS: SARS-CoV-2 nucleocapsid antigen concentrations were measured using a validated microbead immunoassay (Quanterix, NIH/NIAID laboratory) in plasma collected at enrollment from 256 subjects in a prospective observational cohort of hospitalized patients with COVID-19 from 3 hospitals, admitted between March 2020 and August 2021. Relationships between viral antigen concentration and clinical status at 1 week as measured by the World Health Organization (WHO) ordinal scale as well as ICU admission were assessed. Models were adjusted for age and sex, baseline comorbidities including immunosuppression, endogenous neutralizing antibodies, baseline COVID-19 severity, smoking status, remdesivir therapy, steroid therapy, and vaccine status. Missing covariate data were imputed using multiple imputation by chained equations. RESULTS: The median viral antigen concentration for the 35 subjects who deteriorated by 1 week was 4507 (IQR 1225-9665) pg/mL compared to 494 (IQR 18-3882) pg/mL in the 212 subjects who did not (p = 0.0004 Figure a). Using ordinal regression, each doubling in viral antigen concentration was significantly associated with a worse WHO ordinal scale at 1 week (unadjusted OR 1.07, 95% CI 1.02-1.13;adjusted OR 1.10, 95% CI 1.02-1.18). Among 168 patients not in the ICU at baseline, the median viral antigen concentration for the 40 patients who progressed to the ICU was 4697 (IQR 482- 10410) pg/mL vs. 459 (IQR 15-3062) pg/mL in the 128 patients who did not progress to require ICU care (p = 0.0001 Figure b). Using logistic regression, each doubling in viral antigen concentration was significantly associated with ICU admission (unadjusted OR 1.18, 95% CI 1.06-1.32, adjusted OR 1.40, 95% CI 1.11-1.76). CONCLUSIONS: Higher plasma viral antigen concentration at hospital admission is independently associated with a significantly worse clinical status at 1 week and a higher odds of ICU admission among hospitalized patients with COVID-19. This novel finding indicates that plasma viral antigen concentration may identify hospitalized COVID-19 patients at highest risk of short-term clinical deterioration in both clinical practice and research. Results of plasma antigen tests are available within 2-3 hours and could be integrated for identifying hospitalized COVID-19 patients who might benefit from early intervention.