On Sunday night, New York officials reported the first Manhattan case of the 2019 novel coronavirus.

By Wednesday, Gov. Andrew Cuomo had announced four more cases in a 50-year-old lawyer, his wife, his son, his daughter, and the neighbor who drove him to the hospital.

Hours later, the governor confirmed that another family of five, which was linked to the lawyer, had contracted the virus. On Thursday morning, New York Mayor Bill de Blasio announced two new confirmed cases—a man in his 40s and a woman in her 80s—with no connection to travel or other diagnosed patients.

Just hours later, Westchester Communications Director Catherine Cioffi told The Daily Beast that the total number of cases in that suburban county had risen to 21 overnight.

“We did a significant number of tests overnight,” said Cuomo, who tallied the confirmed cases statewide at more than 22, of which he said at least eight were connected to the lawyer in New Rochelle.

Both new Manhattan patients announced by the mayor were hospitalized in the intensive care unit, and the city’s disease detectives were tracing their possible contacts.

“We are going to see more cases like this as community transmission becomes more common,” said De Blasio. “We want New Yorkers to be prepared and vigilant, not alarmed. We are taking the same decisive steps in every case to shut transmission down: isolate and test each suspected case, trace close contacts, and isolate and test them as well.”

As cases of unknown origin spiked in the country’s most populous city, authorities moved to calm the public, closing a Bronx high school and part of a private university in Manhattan out of an abundance of caution. All of the confirmed patients in New York were either in isolation at a hospital or in quarantine at their homes, officials have said.

But as has been widely reported, at least so far, there has been a conspicuous shortage of available and effective diagnostic tests in the United States, even as the same tools had been widely distributed by the thousands in countries like Italy and South Korea. It did not help to assuage public fears about access to the tests when the Centers for Disease Control and Prevention (CDC) this week stopped publicly announcing how many tests had been completed.

And along with supply-chain concerns in such a massive population center, a city like New York may be uniquely vulnerable to a wider outbreak because of easy access to public transportation, and its assorted travel hubs.

“COVID-19 spreads like a common cold through sneezing, coughing, and sharing nasal secretions,” said Dr. Jeffrey Klausner, an adjunct professor of epidemiology at UCLA who previously worked at CDC. “Close contact like in crowded transportation could help increase that spread.”

In response to the largest outbreak in the U.S., including 10 deaths, health authorities in Washington state on Wednesday began recommending—but are not requiring or mandating—that high-risk individuals stay home and avoid large groups, including public places.

King County Executive Dow Constantine told reporters that those recommendations should apply to people 60 and older; those with underlying health conditions like heart disease, lung disease, or diabetes; people who have weakened immune systems; and people who are pregnant.

Health officials also used a Wednesday press conference in the Seattle area to encourage all county businesses to allow telecommuting to as many employees as possible.

The CDC guidelines for triggering social-distancing measures reportedly vary based on any given virus’s severity, contagiousness and mortality rate, which is measured on a scale from one (seasonal influenza, for example) to five. Voluntary home isolation and quarantine are not normally recommended until an outbreak hits category three, followed by school closures at category four or five. Even in a category five, essential services in New York, like the power grid and even some public transportation, would continue to operate, according to New York magazine.

But the response to the outbreak in Washington state may shed light on what New Yorkers can expect in the coming weeks and months, if the spread of the virus continues.

Do you know something we should about 2019 novel coronavirus, or how your local or federal government is responding to it? Email Olivia.Messer@TheDailyBeast.com or securely at olivia.messer@protonmail.com from a non-work device.

Though it’s tough to predict if or when authorities in New York would want to implement those same measures, Klausner said “some might suggest” social distancing of that magnitude at more than 1,000 cases per day for at least three days in a row. But he cautioned that “New York is a much larger and more complex population” to handle.

“I think that advice is going to come very soon,” said Dr. Adrian Hyzler, chief medical officer for Healix International, which provides medical information to travelers. “We’ve come to appreciate that this virus is a lot more contagious than was initially hoped.”

As authorities recommended in Washington on Wednesday, Hyzler said it would be wise, even at this point, for New Yorkers “to stagger your journey times to avoid the busiest times if possible when the trains are packed.”

Some of the supply issues facing a giant metropolis—like the test kits, along with mechanical ventilators and masks—are simply not within the city’s control, and are faced by all major urban centers, experts said.

“New York City is hampered by the same thing that the rest of the country is hampered by: The extraordinary delay in getting testing kits,” said Irwin Redlener, director of the National Center for Disaster Preparedness at Columbia University and an expert on U.S. readiness for pandemics. “There were all sorts of technical problems that should not have happened. At some point, there needs to be a serious investigation into what went wrong and why the U.S. took so long to get its act together on this.”

“We’re all sort of scrambling to make up for lost time,” said Redlener. “We’re way behind where we should be.”

The Department of Health and Human Services said on Wednesday that the United States has only 1 percent of the required respirator masks needed—just for medical professionals—if the outbreak were to become a pandemic. The nation’s emergency stockpile of drugs and medical supplies currently holds about 12 million medical-grade N95 respirator masks and 30 million surgical face masks, out of a need for about 3.5 billion.

Also on Wednesday, the World Health Organization officials urged medical supply manufacturers to “urgently increase production” to meet the global demand, CNBC reported.

Redlener said he was in meetings with New York Mayor Bill de Blasio on Tuesday, where he was “pleasantly surprised” by the city’s actions, especially when it comes to basics like manpower.

“But we should have far more tools and assets than we currently have,” he added. “If it really gets significantly worse as a pandemic, we could find ourselves with a serious shortage of mechanical ventilators and antibiotics and other things that we’ll need.”

According to a laundry list of actions announced by de Blasio’s office, the city’s Department of Health and Mental Hygiene instituted an early detection system for the virus for deploying disease detectives; launched a $6.5 million subway, digital, and multi-media campaign to encourage hygiene for people to seek care if they’re symptomatic; and activated an incident command system to focus agency resources. At the same time, New York City Health + Hospitals activated its Emergency Operations Center after conducting drills across all 11 emergency departments to assess readiness. The Fire Department of New York has also implemented call screening for potential 2019 novel coronavirus cases, where dispatchers may ask about symptoms and travel history, so that responders may be equipped with proper protective equipment in the event of a coronavirus case.

The city’s Department of Education, meanwhile, increased the frequency of deep-cleans on campuses; moved to ensure all 1,800 schools have adequate hygiene and cleaning materials; sent updated federal guidance home to families; and advised cancelling study abroad programs and agency-sponsored school trips to countries with level 2 or higher advisories like China, South Korea, Italy, Iran, and Japan. The city’s plans also included distributing educational materials on safe hygiene practices to all clients and employees at social services shelters, as well as updated clinical protocols for intake—and the event that symptoms pop up among inmates—correctional facilities.

Still, even de Blasio pointed to questions about sufficient equipment for a worst-case scenario.

“To ensure we are able to test as many people as possible, we urgently need the CDC to increase our supply of COVID-19 test kits and expedite the approval of any testing approaches developed by private companies,” he said Thursday. “Our single greatest challenge is the lack of fast federal action to increase testing capacity—without that, we cannot beat this epidemic back.”

And the unique reliance of so many millions on a dense public transit system loomed especially large. “The probability of cross-contamination is very high,” said Oren Barzilay, President of FDNY EMS Local 2507.

Echoing Redlener and de Blasio’s concerns about supplies, Barzilay expressed concern New York simply doesn’t have the resources to deal with an outbreak of epidemic proportions, especially when fear takes over.

“When people panic, calls will start coming in for a regular flu,” he said.