Scientific research

How early can COVID-19 be transmitted before symptom onset?

Nature Medicine has published the latest research on pre-symptomatic transmission of COVID-19 by Eric Lau, Peng Wu, Ben Cowling and Gabriel Leung. They estimated that an infected individual would be able to transmit the virus as early as 2-3 days before symptom onset, resulting in 44% of secondary cases secondary cases being infected during the index cases’ pre-symptomatic stage. Besides, high viral loads were detected soon after symptom onset and would gradually decrease towards the detection limit at about 21 days after symptom onset. Given a substantial proportion of pre-symptomatic transmission, measures such as enhanced personal hygiene and social distancing are encouraged which would play an important role in community disease control.

Read more about this paper here:

# transmission dynamics


©2020 - Coronavirus disease (COVID-19) - School of Public Health, The University of Hong Kong. All rights reserved.