It is estimated that viral shedding — which is when a person infects another — starts happening two to three days before the onset of symptoms. (Source: Max Planck Institute)
A study from China has come to the conclusion that 44 per cent of those who tested positive contracted the disease from an asymptomatic person. They estimated that viral shedding — which is when a person infects another — starts happening two to three days before the onset of symptoms.
The study, published in Nature Medicine on April 15, looked at 94 patients with laboratory-confirmed COVID-19 admitted to Guangzhou Eighth People’s Hospital and said, “We observed the highest viral load in throat swabs at the time of symptom onset, and inferred that infectiousness peaked on or before symptom onset. We estimated that 44%... of secondary cases were infected during the index cases’ presymptomatic stage, in settings with substantial household clustering, active case finding and quarantine outside the home. Disease control measures should be adjusted to account for probable substantial presymptomatic transmission
Presymptomatic transmission of 48% and 62% have been estimated for Singapore and Tianjin, noted the researchers who included those from Guangzhou Medical University and the World Health Organization Collaborating Centre for Infectious Disease Epidemiology and Control at the University of Hong Kong