Coronavirus Antigen Levels Associated With COVID-19 Severity

Carolyn Crist

August 30, 2022

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The levels of SARS-CoV-2 antigen in the blood of hospitalized COVID-19 patients appear to line up with how severe the illness is and other clinical outcomes, according to a new study published in the Annals of Internal Medicine.

Antigens are molecules that are not part of your body that cause your immune system to react, producing antibodies to fight the invader. SARS-CoV-2, the virus that causes COVID, carries antigens.

Higher antigen levels could mean the virus is reproducing and the disease is more severe, the study authors said. As a result, antigen levels could potentially be used to predict which patients may have a higher risk of more severe COVID-19, as well as who could benefit from certain treatments.

"These results suggest that a precision medicine approach to inpatient COVID-19 clinical trials is needed, with a substantial portion of patients hospitalized with acute SARS-CoV-2 infection potentially more likely to benefit from antiviral therapy," the study authors concluded.

Researchers from the National Institute of Allergy and Infectious Diseases and several U.S. universities analyzed the levels of virus antigen in blood samples from 2,540 hospitalized COVID-19 patients enrolled in the Therapeutics for Inpatients with COVID-19 trial. They focused on patients who had up to 12 days of symptoms between August 2020 and November 2021, before the Omicron variant became dominant.

The researchers measured a coronavirus-specific antigen in the blood, as well as whether the patient had gotten the Delta variant. They looked at the time to release from the hospital and symptoms related to the lungs on the fifth day of the clinical trial.

The research team found a strong link between coronavirus antigen levels of 1,000 nanograms per liter or higher and worse lung function at the time the patient enrolled in the trial. Those with higher antigen levels also generally had worse lung function at day 5, regardless of how severe their illness was at the time they enrolled. Antigen levels were also higher among patients with more than a week of symptoms.

Average antigen levels were three times higher among those who needed noninvasive ventilation or oxygen, as compared with those breathing room air. About 26% of patients with antigen levels of 1,000 nanograms per liter or higher ended up needing oxygen by day 5, as compared with 6% of those with antigen levels of 1,000 nanograms per liter or lower.

Patients with higher antigen levels also had longer hospital stays. They averaged about 7 days in the hospital, as compared with 4 days in the hospital for those with lower antigen levels. Among patients on ventilation or oxygen, about 42% of those with high antigen levels were released by day 28, as compared with 73% of those with low antigen levels.

Several risk factors appeared to be linked to antigen levels. Men and adults over age 65 were more likely to have high antigen levels and worse outcomes. What's more, patients who got the Delta variant had higher antigen levels than those infected with variants that were dominant before Delta.

Patients who had coronavirus antibodies from vaccination or a previous illness were more likely to have lower antigen levels, as well as those who had 2 or more days of exposure to remdesivir, an antiviral medication.


Annals of Internal Medicine: "The Association of Baseline Plasma SARS-CoV-2 Nucleocapsid Antigen Level and Outcomes in Patients Hospitalized With COVID-19."


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