A woman checks her son's forehead on January 27, 2020 in Wuhan, China. The city remains on lockdown for a fourth day. Photo by Getty Images

There is not yet “any clear evidence” that people can transmit the Wuhan coronavirus before they begin exhibiting symptoms, Dr. Nancy Messonnier, director of the US Center for Disease Control and Prevention's National Center for Immunization and Respiratory Diseases, told reporters on Monday.

But, she said, it’s a possibility health officials are investigating.

Messonnier’s comment comes after China's health minister Ma Xiaowei said people can spread the virus before they become symptomatic, but offered no explanation as to why he believes that to be the case.

"At this time, it’s unclear how easily or sustainably this virus is spreading between people,” the CDC says.

The CDC has based early theories about the novel virus on what we know about SARS and MERS, which are part of the same family of viruses. Based on that knowledge, the CDC also believes that symptoms of the Wuhan coronavirus may take anywhere from two days to two weeks after exposure to show symptoms. It is also thought to transmit chiefly through droplets from coughs or sneezes, consistent with comments made Monday by Chinese officials.

On the call with reporters, Messonnier also seemed to allay concerns that the virus could be transmitted via packages sent from China. Coronaviruses like SARS and MERS tend to have poor survivability, and there’s “very low, if any risk” that a product shipped at ambient temperatures over a period of days or weeks could spread such a virus.

“We don’t know for sure if this virus will behave exactly the same way,” Messonnier said, but there’s no evidence to support transmission of the virus via imported goods.

Messonnier repeated her message that the immediate risk to the US public is low at this point.