China enacted its travel ban on January 23rd, in an effort to get its arms around the spread of COVID-19.
But according to Business Insider, a new study claims 86% of coronavirus infections in China went undiagnosed before then.
Those who don't get diagnosed often have mild or even non-existent symptoms.
The study says people who hadn't been diagnosed with the virus were the source of 79% of reported cases there.
Therefore, if undiagnosed people hadn't spread the virus, the number of cases could have been reduced by 66% in Wuhan and 79% across all of China.