SARS-CoV-2 Plasma Antibody and Nucleocapsid Antigen Status Predict Outcomes in Outpatients With COVID-19.

Background: Reliable biomarkers of coronavirus disease 2019 (COVID-19) outcomes are critically needed. We evaluated associations of spike antibody (Ab) and plasma nucleocapsid antigen (N Ag) with clinical outcomes in nonhospitalized persons with mild-to-moderate COVID-19.
Methods: Participants were nonhospitalized adults with mild-to-moderate COVID-19 enrolled in ACTIV-2 between January and July 2021 and randomized to placebo. We used quantitative assays for severe acute respiratory syndrome coronavirus 2 spike Ab and N Ag in blood and determined numbers of hospitalization/death events within 28 days and time to symptom improvement.
Results: Of 209 participants, 77 (37%) had quantifiable spike Ab and 139 (67%) quantifiable N Ag. Median age was 50 years; 111 (53%) were female, 182 (87%) White, and 105 (50%) Hispanic/Latino. Higher risk of hospitalization/death was seen with unquantifiable (22/132 [16.7%]) versus quantifiable (1/77 [1.3%]) spike Ab (risk ratio [RR], 12.83 [95% confidence interval {CI}, 1.76-93.34]) and quantifiable (22/139 [15.8%]) vs unquantifiable (1/70 [1.4%]) N Ag (RR, 11.08 [95% CI, 1.52-80.51]). Increasing risk of hospitalizations/deaths was seen with increasing N Ag levels. Time to symptom improvement was longer with unquantifiable versus quantifiable spike Ab (median, 14 [interquartile range {IQR}, 8 to >27] vs 8 [IQR, 4-22] days; adjusted hazard ratio [aHR], 0.66 [95% CI, .45-.96]) and with quantifiable versus unquantifiable N Ag (median, 12 [7 to >27] vs 10 [5-22] days; aHR, 0.79 [95% CI, .52-1.21]).
Conclusions: Absence of spike Ab and presence of plasma N Ag predicted hospitalization/death and delayed symptom improvement in COVID-19 outpatients.
Clinical Trials Registration: NCT04518410.
Competing Interests: Potential conflicts of interest. N. J. received salary support to the institution from Sagent Pharmaceuticals. D. A. W. has received funding to his institution to support research and honoraria for advisory boards and consulting from Gilead Sciences. T. H. E. serves as a consultant for Tonix Pharmaceuticals. E. S. D. receives consulting fees from Gilead Sciences, Merck, and GSK/ViiV and research support through his institution from Gilead Sciences and GSK/ViiV. J. Z. L. has received research funding from Merck. J. J. E. is an ad hoc consultant to GSK/VIR, data monitoring committee chair for Adagio Phase 3 studies. J. S. C. has consulted for Merck and Company. D. M. S. has consulted for Fluxergy, Kiadis, Linear Therapies, Matrix BioMed, Arena Pharmaceuticals, VxBiosciences, Model Medicines, Bayer Pharmaceuticals, Signant Health, and Brio Clinical. K. W. C. received research funding to the institution from Merck Sharp & Dohme and is a consultant for Pardes Biosciences. All other authors report no potential conflicts. All authors have submitted the ICMJE Form for Disclosure of Potential Conflicts of Interest. Conflicts that the editors consider relevant to the content of the manuscript have been disclosed.
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