P206: SARS-CoV-2 Viral Levels and Antibody Response in Mildly Symptomatic and Asymptomatic Participants
Director, Scientific Affairs
Celerion United States
More than 2 years into the COVID-19 pandemic, there is still limited data available on viral levels in mildly symptomatic and asymptomatic infected individuals. This observational trial evaluated SARS-CoV-2 viral kinetics and antibody response in otherwise healthy adults positive for COVID-19.
Participants detected for SARS-CoV-2 during routine screening were enrolled in an 8-week study. Ultrasensitive saliva and extraction-free nasopharyngeal SARS-CoV-2 PCR assays were validated for paired specimen analysis, and immune response was evaluated with a serum spike protein antibody assay.
The nasopharyngeal and saliva PCR assays were established using 2019-nCoV selected from nucleocapsid gene and human RNase P gene prime-probe sets. Both methods demonstrated good precision and reproducibility, with 100% reproducibility established for Within-Assay, Between-Assay and Between-Operators. The limit of quantification ranged from 0.5-10,000 genome copies/µL. When comparing PCR results against a commercial diagnostic test, our ultrasensitive assay demonstrated excellent performance determined by an area-under the receiver operator curve (AUROC) of 93%. Assay sensitivity and positive predictive value were 90% and 86%, respectively.
The assays were applied in a clinical observational trial that enrolled 30 participants (11 males / 19 females). Twenty percent were completely asymptomatic, while the remaining reported mild symptoms of persistent cough, congestion or runny nose, new loss of taste and/or smell, and brain fog. Nonlinear regression modeling of asymptomatic data demonstrated lower SARS-CoV-2 RNA levels throughout the study compared to symptomatic counterparts for both nasopharyngeal (p=0.004) and saliva (p<0.0001) samples. On the other hand, antibody response was similar between the two groups. Interestingly, when subdividing symptomatic subjects by the number of symptoms experienced, participants reporting >5 symptoms displayed the highest SARS-CoV-2 RNA levels accompanied by the lowest antibody response.
We validated sensitive and robust assays to detect and monitor SARS-CoV-2 viral levels from nasopharyngeal and saliva samples. These methods demonstrated excellent performance and positive predictive value against a commercial diagnostic test. Furthermore, our assays were able to detect differences in the viral kinetics between asymptomatic and mildly symptomatic COVID-19 infected subjects. Overall, these findings demonstrate that higher viral levels are associated with a greater number of COVID-19 symptoms, and may suggest a certain viral level threshold is needed to induce symptoms in otherwise healthy adults. As more variants of the virus emerge, the relationship between viral load and symptoms warrants further exploration.