The coronavirus virus spreads quickly and stealthily, supporting the argument for extreme containment measures, say infectious disease specialists at the University of Texas at Austin.

The researchers studied hundreds of case reports from 93 Chinese cities. They determined that the time between cases in a chain of transmission is about four days. That’s the average time between symptoms appearing in a person who transmits the virus to symptoms showing in the person they transmit it to.

Furthermore, more than 10% of patients are infected by somebody who does not yet have symptoms, they found.

“The short serial interval of COVID-19 means emerging outbreaks will grow quickly and could be difficult to stop,” said Lauren Ancel Meyers, Ph.D. “The data suggest that this coronavirus may spread like the flu. That means we need to move quickly and aggressively to curb the emerging threat,” she wrote in a paper in press with the journal Emerging Infectious Diseases.

The findings align with other evidence showing that undetected cases probably drove the rapid spread of the COVID-19 outbreak in China. Scientists from Columbia University estimate that 86% of all infections were undocumented in the early weeks of the outbreak in Wuhan province, and those infections were likely responsible for fully two-thirds of the documented cases.

“The explosion of COVID-19 cases in China was largely driven by individuals with mild, limited, or no symptoms who went undetected,” said Jeffrey Shaman, Ph.D., from the Columbia University Mailman School of Public Health. “Depending on their contagiousness and numbers, undetected cases can expose a far greater portion of the population to the virus than would otherwise occur.”

Taken together, the latest evidence means that control measures such as those taken by state and federal officials in recent days are warranted, said Meyers. These include isolation, quarantine, school closures, travel restrictions and cancellation of mass gatherings.

The data may offer a different picture over time, as new cases emerge worldwide each day, the University of Texas at Austin team cautioned.