As morning dawns in Wuhan, a huge city in central China, train stations and airports are closed, roads blockaded, and the 11 million residents, many of whom were preparing for Lunar New Year trips, have been warned not to leave. The quarantine, enacted Thursday following the rapid spread of a deadly coronavirus that has already infected more than 500 people, is an unprecedented step—the equivalent of closing down Chicago in the middle of the night two days before Thanksgiving. The move was prompted by an outbreak that has already reached as far as the United States, Thailand, Japan, and South Korea.

But it’s not the residents of Washington state or Bangkok who are most at risk from the coronavirus. It’s China’s poor—as in many countries, a critically underserved population when it comes to health care. It’s the poor who were most likely to be in contact with the virus, it’s the poor among whom it will spread fastest, and it’s the poor who will likely be the main victims of over-repressive measures as the government, after weeks of what looked like a cover-up, snaps to action.

The Wuhan coronavirus appears to have emerged through animal-to-human contact in the Huanan Wholesale Seafood Market. Despite the name, the market sold a huge range of wildlife delicacies, from wolf cubs to the snakes or bats now believed to have been the initial vector of infection. As in other live markets, the dirty, dangerous work of handling the animals was chiefly done by ordinary workers, many of them migrants. Wuhan—itself a massive city formed from the merger of the three towns of Wuchang, Hanyang, and Hankou—is finding that its size has become a liability.

During the late 20th century, real estate developments grew the city’s economy and enveloped suburban townships in surrounding areas of Hubei province. Wuhan’s health care system now strains to handle the full brunt of a health crisis impacting the entirety of its population. Within this community, many migrants and college students on its many university campuses had already departed the city by the time the Jan. 23 quarantine was set. Now, as other regions of China struggle to calculate and report coronavirus cases from travelers taking their annual sojourn home, treatment and public health information has become the top policy priority for officials.

Despite the vast scale of this problem’s domestic dimension, word of cases in South Korea, Thailand, and other far-flung locations arrived far before reports of the spread of the infection to Wuhan’s neighboring cities and towns. In all of those cases, of course, the travelers who carried the virus were far better off than the average Chinese citizen—simply by virtue of having the resources to travel abroad. (Less than 10 percent of China’s population owns a passport.) Middle-class travelers coughing in economy class to Bangkok were far easier to detect than the sweating worker riding a shared truck back to the edge of Wuhan or taking a long-distance bus home to another province in advance of the Lunar New Year this Saturday. Because of the nature of the service sector and dearth of labor benefits, many migrants may have been reluctant to abandon their sole chance for family reunions.

China is a surveillance society, but the net of surveillance has massive holes. Middle-class Chinese lives are highly visible to technological profiling systems, the poor much less so. Some do not even possess an ID card, supposed to be carried by all citizens at all times—either because they’ve lost them and been unable to replace them without an expensive trip to their hometown or because their birth was never registered with the government. Instead of traveling by train or plane, which require ID checks, they take difficult-to-monitor long-distance buses or use informal truck and van transport networks. Even their online presence is severely curtailed; despite claims that services like WeChat are ubiquitous, internet penetration in China is only around 60 percent. Resources such as WeChat accounts or ID cards are sometimes pooled between families, with parents making use of children’s identities.

With rural areas often left in the dark, slower to receive preventative measures on hand-washing, face masks, and other health news, families with phones and good internet connections have an edge in finding out what to do to stay healthy. As the coronavirus makes its way outside of Wuhan, public health resources also thin out, and medical supplies may be slower to reach more distant hospitals for adequate treatment. Mask shortages in Shanghai and beyond have emerged at a time when manufacturing facilities wind down for the Lunar New Year. One mask factory is offering three times regular wages for workers to return from holiday. These supply scarcities, in conjunction with previous inequities, will divide preventative capabilities between the haves and the have-nots.

The poor affected by the virus are also much less likely to have seen a doctor. China’s health care system, which combines public and private elements, is notoriously challenging to navigate even for middle-class patients. Large portions of the population have little or no access to quality health care. Even when rural or small-town resources are nominally available, resources are clustered, as per policy, into larger cities and metropolises. Most Chinese doctors are only educated to the undergraduate level, sometimes even less, and actual Doctors of Clinical Medicine (the equivalent of an American M.D.) almost exclusively work in large city hospitals, which are now filled to the brim with patients and staff increasingly stretched thin.

While public insurance exists, and has been expanded in recent years, it is also linked to the hukou—China’s ubiquitous residence permit that citizens are born into. This policy challenge makes it impossible for rural residents to use their insurance in city hospitals with more qualified staff or for migrant workers, who usually work far from where they hold a hukou, to access the system at all. As a result, they avoid using medical services except in dire need, often self-medicating—one reason for China’s tremendously high usage of over-the-counter antibiotics—or turning to traditional Chinese medicine practitioners. Their often relatively poor health makes them more vulnerable to the virus and more likely to mistake it for a regular cold or flu.

All these factors are exacerbated by age. From the limited data released, retirees – with a median age of 75 –  make up the vast majority of the 17 dead so far, and older individuals with preexisting respiratory conditions remain among the most at risk. But migrant workers, lacking access to proper pensions and good-quality care, can often be in their 40s, 50s, or older—and in worse condition, thanks to a lifetime of hard labor, than their middle-class counterparts.

The relative invisibility and perceived lack of importance of the poor may be one reason why the official number of cases—as of writing, more than 500—differs widely from the estimates produced by foreign modeling of 1,700 or more. The system may simply have not been able to find patients, rather than covering up their existence. (Some mixture of the two is most likely.)

The sudden rush of attention last weekend may go some way to fixing this, with free—or mandatory—diagnosis throughout the city and other key transport hubs. But these resources are likely to be concentrated in the urban core—and are already badly overstretched, with reports of packed corridors and dangerously exhausted medical personnel. In the aftermath of past natural disasters, such as the Sichuan and Tangshan earthquakes, the state also tends to neglect the countryside in favor of the cities, leaving rural people to fend for themselves. Within Wuhan itself, residents are highly reliant on public transportation, including bus, subway lines, and ferries, which have now been shut down. Lower-income nurses, junior-level doctors, and hospital personnel may find it harder to travel to necessary job shifts.

The poor may be less visible for diagnosis and treatment, but they’re more visible for repression. As the quarantine tightens around Wuhan, meanwhile, the poor are also far more likely to be the victims of brutality by the authorities. Disaster often brings with it elite panic, singling out the poor or outsider groups. After the Tangshan earthquake in 1976, urban militias beat to death or shot country dwellers coming into the city seeking aid, claiming they were looters. If fear—among the armed men who will have to enforce the quarantine or among the population trapped inside—spreads, these kinds of deadly confrontations may emerge, especially as supplies for treatment and ongoing day-to-day activities within a sealed-off Wuhan dwindle. Disinformation has also emerged as both imposing risks and slower public response and as a vector for law enforcement crackdowns on “rumormongers.” As with other cases of Chinese law enforcement, the line between spreading fake information and criticism of the government remains blurred.

While the quarantine may help halt the spread of the virus, working-class Chinese—especially migrants—least visible to the system are already beyond the reach of even the most ideal public health campaign. The Lunar New Year vacation may begin Friday, but migrant workers often begin their travels far earlier than white-collar workers—not least because they have longer and tougher journeys. Finding them—and helping them—will be a huge challenge but an essential one.