COVID-19 may be most contagious one to two days before symptoms appear
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 percent 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 appear, researchers suggest April 15 in Nature Medicine. Scientists swabbed the noses of 94 coronavirus patients who were admitted to the Guangzhou Eighth People’s Hospital in China from January 21 through February 14. Amounts of the virus’s genetic material peaked quickly after the onset of symptoms, then declined over about 21 days, the team found. That 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...