Skip to main content
NIH Record - National Institutes of Health

SARS-CoV-2 Antigen Levels Linked to Patient Outcomes

Many clusters of small red balls (Covid particles) around human tissue (blue)

Colorized scanning electron micrograph of a cell infected with the Omicron strain of SARS-CoV-2 virus particles (red), isolated from a patient sample

Photo: NIAID

In a new study, NIAID researchers analyzed levels of SARS-CoV-2 antigen in blood samples taken from study participants and assessed the association of those levels with disease progression. 

Following the ACTIV-3 trial of Covid-19 therapeutics in people hospitalized with the virus, researchers found the amount of SARS-CoV-2 antigen measured in their blood was associated with illness severity and other clinical outcomes. The results were published in the Annals of Internal Medicine.

Higher levels of viral antigen in the blood, which could indicate ongoing SARS-CoV-2 replication, correlated with more severe disease. The authors suggest that SARS-CoV-2 antigen levels hold promise as a biomarker, or a measurable substance, to predict which patients hospitalized with Covid-19 have a higher risk of worse outcomes.

The ACTIV-3 trial enrolled people hospitalized with Covid-19 between August 2020 and November 2021. Participants contributed a baseline blood sample and were then randomized to receive either an experimental Covid-19 therapeutic or a placebo. All participants received the antiviral remdesivir unless contraindicated. In this follow-up analysis, the researchers examined 2,540 participant baseline blood samples for SARS-CoV-2 antigen levels.

Researchers assessed the relationship between each participant’s SARS-CoV-2 blood antigen levels and their time to discharge from the hospital, as well as their pulmonary symptoms at day 5 of the trial.

The analysis revealed a strong correlation between higher SARS-CoV-2 antigen levels (≥1000 nanograms per liter) and worse pulmonary function at the time of enrollment. Importantly, participants with higher SARS-CoV-2 antigen levels in the blood at enrollment generally had decreased pulmonary function at day 5, regardless of the severity of their illness at the time of study entry and took longer to be released from the hospital. 

Three additional participant characteristics were found to correlate with lower antigen levels: the presence of SARS-CoV-2 antibodies, exposure to remdesivir prior to enrollment and longer time in hospital prior to enrollment. Finally, participants infected with the delta variant had higher antigen levels than those infected with prior circulating strains. 

The researchers concluded that measuring antigen levels in the blood could be useful for predicting a patient’s disease progression and likely outcomes once they are admitted to the hospital.

Back to Top