Shoppers have rushed to stores in Toronto, Chicago, New York, and elsewhere, buying out all the face masks as coronavirus cases began emerging across the globe. As of Tuesday, the US had only five confirmed cases and Canada had just one, but some people don’t like to take any chances. They want protection.

The sell-out of protective gear that was likely made in China—to protect us from a virus coming from China—is a kind of metaphor for a much deeper supply issue posed by the outbreak. Every day, people rely on Chinese companies for life-saving products. The country is the world’s largest producer of active pharmaceutical ingredients, even if the finished medications get put together in the US or another country. Although it’s too soon to feel any repercussions, the coronavirus outbreak adds uncertainty to that supply.

“This outbreak just underscores what can happen in a worst-case scenario,” says Amesh Adalja, an infectious disease physician at the Johns Hopkins Center for Health Security, who has warned about the national security implications of a heavy dependence on China and other countries for vital medicine and medical supplies. “Any kind of supply shock or instability would render the drug supply vulnerable,” he says. “With this outbreak, it is concerning whether or not the stability of our supply chain will remain intact.”

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Wuhan is not China’s largest site for pharmaceutical manufacturing, but the city, once known for its heavy industry and steel, has become a burgeoning center for bio-pharmaceutical research and development. Transportation in and out of the central Chinese city of 11 million, in Hubei Province, has been shut down—roads closed, planes grounded, trains halted. Sixteen cities in Hubei Province have similar travel bans. Shanghai has extended its Chinese New Year holiday, keeping businesses closed through February 3. Other countermeasures are likely as the outbreak evolves.

Drug manufacturers are required to notify the US Food and Drug Administration of supply disruptions. “At this time, manufacturers have not reported any impact and we will continue to be in communication with manufacturers,” the agency said in a statement. But because China ships raw materials to pharmaceutical plants around the world, which maintain some inventory of ingredients, it may take months for any shortages to affect supply, says Erin Fox, a pharmacist and expert on drug shortages at the University of Utah Health.

The biggest problem is that there is no publicly available information on what portion of which critical medicines originate in China, and specifically where those factories are located, she says. Pharmaceutical companies consider such information to be proprietary. “One of the big unknowns is how many products are sole-sourced—in which literally only one place in the world makes that raw material,” she says. “We don’t have good information on that at all.”

China has 15 percent of the world’s facilities that manufacture active pharmaceutical ingredients for 370 essential drugs, while the US has 21 percent of those facilities, according to the FDA. But the agency doesn’t know how much those facilities produce—if they produce anything at all.

That lack of information is unsettling. “What is the threat to our national health care if there is some kind of geopolitical issue or an outbreak like this or some kind of natural disaster? We really don’t know,” says Michael Ganio, director of pharmacy practice and quality at the American Society of Health-System Pharmacists.

Hurricane Maria in Puerto Rico provided a hint. A Baxter manufacturing plant that supplies half of US hospitals with small-volume saline bags was hit by the storm. The company had no redundancy in its manufacturing capacity, and hospitals around the country faced a critical shortage.