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Kai-Wang To, et. al

Published online March 23, 2020


Kai-Wang To et al. present findings of a cohort study to ascertain the serial respiratory viral load and the serum antibody responses of 23 laboratory-confirmed COVID19 patients. They reported that salivary viral load was highest at the onset of symptoms and declined after that. In some patients, viral RNA was detected up to 25 days after symptoms started. There was a positive correlation between age and peak viral load and this peak was higher in severe cases than mild ones. Serum antibody levels against SARS-CoV-2 nuclear protein (NP) and surface spike protein receptor binding domain (RBD) increased 10 days or later after symptoms onset and did not correlate with disease severity.


  1. Self-collected posterior oropharyngeal saliva samples can overcome patients’ discomfort and risks to health-care workers of nasopharyngeal and throat swabs.
  2. Viral load of SARS-CoV-2 is very high at presentation and declines steadily.
  3. Most patients have an antibody response 10 days or later after symptoms onset.
  4. Viral whole-genome sequencing of serial paired samples from single individuals did not detect any viral mutation during the course of infection.


Serum antibody levels against NP and RBD can complement RT-qPCR analysis of saliva viral load.

Self-collection of posterior oropharyngeal samples can inhibit transmission to health-care workers. Pro-longed detection of viral RNA suggests that SARS-CoV-2 might be excreted

despite clinical recovery making patients’ discharge complicated. Antibody response seems to be inversely correlated to viral load so it can be used to make control measures.

Viral load profile of SARS-COV-2 can help guiding antiviral treatment.


Case study

Cohort study of 24 laboratory-confirmed COVID-19 patients, screened between Jan 22, 2020 and Feb 12, 2020. Samples of blood, urine, posterior oropharyngeal saliva, and rectal swabs were collected. Viral load was determined using RT-qPCR and antibody levels against NP and RBD were measured using EIA. Whole-genome sequencing was done using Oxford Nanopore MinION device.



No study of clinical progression of COVID-19 in terms of temporal viral load and serum antibody profiles was reported before. This study highlights the importance of understanding viral kinetics and antibody response for generating therapeutic strategies and infection control policies.


Only 23 patients were included in the study and 48% had chronic medical illness (compared to 24% in large clinical trials). Viral load and antibody titre were not available every day. Patients might not be consistent with the self-collection of posterior oropharyngeal saliva samples. Statistical analysis could not adjust for potential confounding factors affecting viral load and serum antibody levels because of the few patients enrolled.