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For months, health experts on the front lines of the battle against COVID-19 told the world to prepare. The coronavirus is not like influenza, they warned. It is highly transmissible, and far deadlier. It shuts down entire cities, as happened in Wuhan, China, and entire countries, as is happening now in Italy. Instead of heeding these warnings while there was time to halt the contagion, the American government downplayed the risks, and the president offered empty reassurances. “It’s going to disappear,” he said, “like a miracle.”

Absent leadership, many are responding as best they can. Ohio and other states have closed schools. The NBA canceled its season. Disney World shuttered its gates. However, the “cancel everything” strategy can only slow the spread of this disease. It will not stop it.

Americans must prepare for the worst. The country is now likely to enter a mass-casualty scenario. The first priority will be identifying people most urgently in need of care, otherwise known as triage, a practice adopted from battlefield medicine, in which the wounded are quickly sorted. American doctors will soon face this grim and painful reality at hospitals and other care facilities across the country.

Triage is all about efficient use of resources. In war or a natural disaster, when supplies and staff are limited, care must be rationed. The injured are categorized into treatment groups, using colored tags or wristbands to identify priority levels. Green signifies the walking wounded,  patients suffering but not needing instant attention. Yellow is for the more seriously injured whose lives are not yet threatened. Red is reserved for those who will die without immediate treatment. There is a fourth category—black, for those already deceased, or with no chance of survival. Anyone still alive among the black may be comforted, but not treated.

The first time I experienced such an event was in the aftermath of Typhoon Haiyan, in the Philippines, during an assignment with Team Rubicon, a nonprofit that deploys veterans as disaster-relief volunteers. My team arrived at a makeshift clinic, already overwhelmed with injured survivors. One of the most acute shortages was anesthesia. Just days into the relief effort, it became clear that our clinic would run out. I remember cleaning deep wounds, some down to the bone, without painkillers, which were reserved for amputations and major surgeries. I still have nightmares about this. Haiyan, and the failure of authorities to ready supplies, killed thousands. The coronavirus will kill far, far more, and many more will need intensive care. We must steel ourselves for what is coming, and prepare as much as we can, even with the abbreviated time left.

We do have some idea of what to expect. In Italy, hospitals have run out of beds, and equipment shortages have led to agonizing life-and-death decisions. Who most deserves treatment? Is it the young mother of three, who may survive without a ventilator but whose chances will be better with one? Or is it the elderly patient, who will surely die without it? There is a cold science to this, using complicated formulas and terms such as quality-adjusted life years to help doctors make the right calls. But the harsh reality remains: Black wristbands will soon be placed on the living.

With the right preparation, we can limit how often this happens. If we heed the warnings of medical experts. America is, at best, a few weeks behind Italy. Bottlenecks remain, especially when it comes to providing testing kits and stockpiling medical equipment. According to the most recent available data, from 2010, the United States has about 62,000 ventilators in hospitals. Additionally, about 10,000 ventilators are stored in the Strategic National Stockpile, a federal store of emergency supplies and medicines, though the exact number is classified. We will likely need many times that in the coming months.

Slowing the spread of COVID-19 remains an essential strategy, and “cancel everything” is the right approach. But at this point, a mass-casualty event is all but inevitable. Every element of America’s strategic-response capability must be activated now. That means setting up federal medical stations utilizing the Strategic National Stockpile. It means activating National Guard and Medical Reserve Corps units, and ensuring that staff and volunteers are trained to use ventilators and other equipment. Telemedicine and virtual call centers must be rapidly expanded, with staff working from home to answer questions about treatment. The Department of Veterans Affairs, which functions as America’s health-care system of last resort, must immediately prepare to accommodate hundreds of thousands of civilian patients. And we must eliminate cost as a barrier to receiving testing or treatment by fully funding the National Disaster Medical System and granting it the authority to reimburse health-care costs related to the virus.

Above all, Americans themselves need a mindset shift. Triage is coming. Many cases of this disease will be minor, and self-triage will be necessary. We must listen to the experts and treat the sick at home if so advised. We must anticipate the rationing of care, and not take out our frustrations on doctors and nurses who are operating under horrifying circumstances.

The most frightening thing is this: If the outbreak gets as bad as some experts now fear, ventilators will not be the only thing in short supply. We will need more black wristbands than we can bear to imagine.

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