HKUMed on COVID-19

23mar-temporal profile


Temporal profiles of viral load in posterior oropharyngeal saliva samples and serum antibody responses during infection by SARS-CoV-2: an observational cohort study

Published on The Lancet Infectious Diseases, 23 March 2020

SARS-CoV-2 is found in the saliva of infected patients. Dr Kelvin To and his team studied the change in the amount of virus in the body (viral load) in 23 infected people as their disease progressed, by analyzing samples of their saliva collected through coughing or throat clearing. The results, published in the leading medical journal The Lancet, showed that the amount of virus in the body was highest in the first week when symptoms appeared. 

The team also collected blood samples to study these people’s immune response to the virus. Antibodies – the body’s natural defence against the virus – were detected 10 days after symptoms appeared. The amount of virus in the body gradually declined as more antibodies were produced; however, the virus was still detectable in a third of patients after 3 weeks. 

Key takeaways:

  • Patients were most infectious during the first week when symptoms appeared
  • The median time between symptom onset to hospitalization was 4 days
  • Older patients and those with severe disease had a higher viral load 
  • Having an underlying chronic illness did not affect the viral load

Using saliva to test for SARS-CoV-2 was less uncomfortable for patients and safer for healthcare workers than a throat swab. A blood test to detect for antibodies was useful to diagnose SARS-CoV-2 infection in patients with a very low viral load.

Understanding how the viral load and antibody level change with time can guide doctors on antiviral treatment, designing a vaccine and measures to control the infection.