A study published in JAMA Internal Medicine has shown that the risk of COVID-19 transmission to close contacts appears to be higher if they are exposedfrom 2 days prior to 3 days following symptom onset in index patients.

Infected contacts of asymptomatic index patients appeared to have lesser odds of presenting with COVID-19 symptoms. This indicates that quantity of exposure may have a link with clinical presentation among contacts. The study included a population-based cohort of 730 index patients with a diagnosis of COVID-19 in China, from January 8 to July 30, 2020. A total of 8,852 close contacts of the index patients were evaluated for COVID-19 through August 2020. Among the close contacts of 730 index patients, the contacts had the highest risk of COVID-19 if they were exposed between 2 days before and 3 days after the symptoms appeared in the index patient, peaking at day 0. There was a lower risk among contacts exposed on days −6 and −5. The risk was nonstatistically higher among contacts who were exposed on other days… (DG Alerts)