In the period before China enacted travel restrictions, about 86 percent of all new coronavirus infections were undocumented, according to a new study published in Science.
Researchers created a mathematical model to combine reported infection rates in China with people's movements. They used the model to estimate infections in 375 Chinese cities from Jan. 10 to Jan. 23, when travel restrictions were implemented in the Hubei province in China, according to MedPage Today.
The study suggests that only about 14 percent of COVID-19 infections were documented before travel restrictions went into effect, while about 86 percent went undocumented.
This means most of the infections were in people who were showing mild symptoms or none at all, the researchers told MedPage Today.
The study also suggests undocumented infections were the infection source for 79 percent of documented cases before the travel restrictions.
"These people [undetected infected persons] were a major driver of it; they were the ones that facilitated the spread," Jeffrey Shaman, PhD, a study author and professor at Columbia University in New York City, told MedPage Today.