There has been much discussion around how the novel coronavirus, SARS-CoV-2, which causes COVID-19, is transmitted from person to person. How does it spread? How can we monitor, isolate and control the spread of COVID-19? Why is social distancing so important?

A recently published paper, provides new evidence which adds to our understanding of transition dynamics.

The study looked at viral loads in upper respiratory tracts of 18 people from Zhuhai in Guangdong, China. 14 of these people had recently returned to Zhuhai from Wuhan and 4 were ‘secondary infections’ i.e. they had not been to Wuhan. Swabs were taken at regular intervals as the infection progressed.

  • 13 had signs of pneumonia on CT scans
  • 3 required admission to intensive care
  • 15 had mild to moderate illness
  • 1 had no symptoms
  • None had visited the Huanan Seafood Wholesale Market

The paper describes the relationships between the people in the study. For example, one patient worked in Wuhan. He visited his wife, mother and a friend on January 17th. His wife and mother developed symptoms 3 and 5 days later and had virus detected soon after symptoms started. The friend had no symptoms but he too had positive swabs on days 7, 10 and 11 after contact.

The team also looked at viral load in the nose and throat of the patients who had symptoms from the day that their symptoms started. High viral loads were detected very soon after symptom onset, with more in the nose than the throat. There was similarity in the viral load of the symptomatic and asymptomatic patients. This suggests that asymptomatic carries can spread the virus too.

This is different to SARS, which caused a global epidemic in 2002-2003 with over 8000 cases in 25 countries, and suggests that very different case detection and isolation strategies are required to manage and control SARS-CoV-2.

For COVID-19, even people who have mild to moderate symptoms can be highly infectious, and they are very infectious very quickly, perhaps even before symptoms develop or very soon afterwards. This is why social distancing is so important.

Please follow official advice for social distancing, self-isolation or shielding depending on your circumstances.

  • Social distancing is something we should all do to reduce social interaction between people in order to reduce the transmission of coronavirus (COVID-19)
  • Self-isolation is what people should do if they, or someone they live with, develop symptoms that may be caused by coronavirus.
  • Shielding is a measure to protect people who are clinically extremely vulnerable by minimising all interaction between those who are extremely vulnerable and others.

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