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Substantial Coronavirus spread seen before symptoms show

Date: 20 April 2020 Tags: Miscellaneous


In a study published recently, researchers found that people infected with novel coronavirus (SARS-CoV-2) start shedding the virus and therefore transmitting it to others before symptoms show up. 



The study says that substantial proportion of transmission probably occurs even before first symptoms appear in the infected person.



  • Studying 77 infector-infectee pairs, pairs of people who passed on the infection and those who got infected, from publicly available sources, the researchers estimate that 44% of secondary cases were infected when the person was yet to show symptoms.

  • The researchers used information on the timing of symptom onsets in transmission pairs to infer the infectiousness profile of people with COVID-19 and found “substantial transmission potential” before symptom onset.

  • The study suggest that efforts to track down contacts of people with coronavirus infection should include people who have come in contact with the infected person not just after symptoms show up but at least two-three days before the person exhibited symptoms.

  • In the case of the 2003 SARS, infectiousness increased seven-10 days after symptom onset. Hence, virus spread can be reduced once the infected person is quarantined soon after symptoms show up.

  • In contrast, influenza is characterised by increased infectiousness shortly around or even before symptom onset. This makes it difficult to contain the spread by isolating people who have come in contact with the infected person after the person exhibited symptoms.

  • Contact tracing can be still effective in preventing the spread if people who came in contact with the infected person two-three days prior to symptom onset are also located and quarantined.

  • Even when mitigation measures such as lockdown are in place, contact tracing would still has an important role to play, particularly in the case of super-spreading events that may occur in high-risk settings including nursing homes or hospitals.

  • Since the proportion of pre-symptomatic transmission is substantial, maintaining hand hygiene and physical distancing can play an important role in containing virus-spread in the community.

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