The amount of SARS-CoV-2 antibodies in the blood of patients hospitalised with Covid-19 could be used to predict illness severity and other clinical outcomes.
A new study, published in the Annals of Internal Medicine, shows that higher levels of viral antigen in the blood, which could indicate ongoing SARS-CoV-2 replication, correlated with more severe disease.
The study authors suggest that antigen levels could help determine those patients most likely to benefit from therapies directed at fighting the virus.
Analysis of Covid patient blood samples
Researchers from the National Institute of Allergy and Infectious Diseases (NIAID), part of the National Institutes of Health, built on the ACTIV-3 trial of Covid-19 therapeutics in people hospitalised with Covid-19.
The researchers analysed levels of SARS-COV-2 antigen in 2540 samples taken from study participants and compared those levels with time to discharge from hospital, as well as their pulmonary symptoms at Day 5 of the trial.
The researchers then conducted statistical analyses to determine if plasma antigen levels were associated with the participants’ pulmonary function when they gave the blood sample – and whether they could predict how the participants would fare over time. In addition, the researchers examined the relationship between a number of participant and viral characteristics and antigen levels.
Antigen levels a marker of ongoing viral replication
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 and took longer to be released from the hospital.
High blood antigen levels also correlated with some known risk factors for worse illness, such as being male. 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 antigen levels in the blood are likely a marker of ongoing viral replication and could be useful for predicting a patient’s disease progression.