Scientists reveal when people with COVID-19 most infectious

Scientists reveal when people with COVID-19 most infectious

People with coronavirus infections may be most contagious one to two days before they start to feel ill, new research suggests.

What’s more, considering pairs of people in which one person definitely caught the coronavirus from the other, scientists estimate that about 44% of COVID-19 cases may spread from person to person before symptoms appear. The results indicate that efforts to track down contacts of people with COVID-19 should include people encountered several days before a person’s symptoms start, researchers suggest in Nature Medicine.

The result indicates that virus production may be strongest at the start of the infection before the immune system kicks in to kill viruses and produce symptoms.

Analyzing 77 infector-infectee pairs allowed researchers to calculate when people are most contagious. The team estimates that contagiousness starts 2.3 days before symptoms begin and peaks 0.7 days before symptoms start.  

Tracing contacts and isolating cases alone may not be successful at stopping more outbreaks if more than 30% of cases result from presymptomatic or asymptomatic transmission, the authors of the new study say. If that’s the case, more than 90% of contacts would need to be identified to contain viral spread.