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Tags Current Affairs

Coronavirus can be transmitted before symptoms show up

Date: 05 April 2020 Tags: Miscellaneous


A study of seven clusters in Singapore provides some evidence that virus transmission to others (resulting in infection) can happen from one to three days before a person shows symptoms.



Some cases in Singapore and other countries suggest that viral shedding can occur in the absence of symptoms and before symptom onset.



  • The World Health Organization maintains that the risk of getting infected with the novel coronavirus (SARS-CoV-2) from someone with no symptoms at all of Covid19 is “very low”. And it says that it is assessing ongoing research on the period of transmission of the virus.

  • The transmission one to three days prior to onset of symptoms was seen in four clusters, while in three clusters the precise timing of transmission could not be established as the index case and the contacts lived together. 

  • Early detection and isolation of patients and contact tracing are important to contain the spread the virus. However, the existence of presymptomatic or asymptomatic transmission adds a new layer of complexity and challenge in tracing contacts.

  • Looking at the serial intervals (the number of days between symptoms onsets in a primary case and a secondary case) in China, researchers had in a study suggested that 12.6% of transmission was presymptomatic.

  • These findings suggest that to control the pandemic it might not be enough for only persons with symptoms to limit their contact with others because persons without symptoms might transmit infection.

  • These findings underscore the importance of physical distancing in the public health response to the COVID-19 pandemic, including the avoidance of congregate settings.

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