Imagine you are in a small boat far, far from shore. A surprise storm capsizes the boat and tosses you into the sea. You try to tame your panic, somehow find the boat’s flimsy but still floating life raft, and struggle into it. You catch your breath, look around, and try to think what to do next. Thinking clearly is hard to do after a near-drowning experience.

You do, though, realize two important things: First, the raft is saving your life for the moment and you need to stay in it until you have a better plan. Second, the raft is not a viable long-term option and you need to get to land.

In April 2020, the storm is the Covid-19 pandemic, the life raft is the combination of intense measures we are using to slow the spread of the virus, and dry land is the end to the pandemic.

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The U.S. is still in the clambering-into-the-life-raft phase of responding to Covid-19, and thinking clearly about what to do is still difficult. This confusion has made it hard to appreciate two facts: One is that social distancing combined with scaling up testing, production of medical equipment, and other countermeasures are essential and must be replicated across the country, intensified, and continued. The other is that if these measures have the desired effect of reducing the number of new cases accumulating each day, they provide only a temporary solution.

We still need to find a way to bring the pandemic to a permanent conclusion.

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Several countries in Asia controlled their epidemics before a majority of the population was infected. Some, like Taiwan and Singapore, did so by containing infections from the start. Others, like China and Korea, did so only after large outbreaks. The control they have reached is only a life raft, not dry land, because unless there have been extraordinarily high levels of infection that were so mild as to go unnoticed, most people in these countries remain susceptible to infection.

Viruses do not remember they were previously under control and will resurge when restrictions are lifted. Just look at what happened in 1918, when cities that had cracked down on the transmission of influenza lifted their restrictions and flu transmission rose again. Mathematical models of Covid-19 by our group and others that incorporate these lessons show that, in the short term, social distancing and other interventions can reduce the impact of the virus. But the same models show that when these interventions are eased, the problem returns.

Let’s be clear. With something like Covid-19 there is the first peak, and there’s the whole epidemic. For the first peak, the evidence so far points to a worrisome possibility of overwhelming our intensive care units — even with the degree of social distancing we’ve achieved — as we’re seeing in New York City. But every bit we slow and flatten the curve will make that less likely and less dramatic, if and when it happens.

It is very possible that after this first wave subsides, we will still have a largely susceptible population, though that depends on how well the social distancing works. Effective treatments and increased ICU capacity could reduce the demand for critical care, lightning the load on the health system, but again, these measures only delay things.

If the SARS-CoV-2 virus has a contagiousness of three, meaning every case infects three other people, then we won’t get to the end of the epidemic until two-thirds of the population has become immune by infection or by vaccination. Successful control of the first peak of infections could leave a majority (perhaps a large majority) of the U.S. population still susceptible to the virus.

There are several broad ideas for how to get to dry land, which is widespread immunity in the population. But each has enormous problems.

One way is to let up on social distancing soon and let the epidemic run its course. That would lead to many deaths and completely overwhelm health care systems around the country. Another way is to maintain intense social distancing until there is a vaccine — but the arrival of a vaccine is uncertain and, absent a miracle, will likely take more than a year. Meanwhile, society and the economy would suffer.

If the first wave really is controlled, another option would be to try multiple rounds of social distancing: instituting it to bring the epidemic under control then letting up, perhaps only in certain areas, to allow cases to occur and immunity to accumulate gradually in the population, and then again introducing another round of social distancing. Our model of this process shows that it would take multiple rounds and would be challenging to accomplish without errors that lead to ICU overload. It would also be difficult to maintain the political and social will to implement this.

The most ambitious approach would be to intensify social distancing and scale up testing until we have the ability to know about nearly every case of Covid-19, trace his or her contacts, and control the spread of the disease one case at a time. This, though, is hard to envision. Even though Singapore detected the infection early, Covid-19 has stretched the island’s public health system to the limits, and our public health system has not had the practice and the resources devoted to stopping a pandemic that Singapore has invested since it faced down severe acute respiratory syndrome (SARS) in 2003. And continued risk of imported cases of Covid-19 from elsewhere in the world — or even from other parts of the country — would lead us in this best-case scenario to restrict and intensively screen travelers for an extended period.

As epidemics and responses to them are local, the scenario in one part of the U.S. could differ from that in another. A report from the Institute for Disease Modeling suggests that even Seattle’s relatively prompt response may have only slowed the spread of the infection and it may see a single-peaked epidemic with much of the population infected, despite social distancing efforts. If accurate, recently reported fever data from a networked thermometer company that illness rates may be coming down, not just growing more slowly, then we may see a second peak once social distancing efforts are lifted.

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Clearly, we need more testing to understand each region’s epidemic trajectory.

A vaccine is ultimately our best hope, but that is in the future — many months away, if not a year or more, in the rosiest scenarios.

Whatever path we choose — and it may be a mix of paths in different parts of the country, as the local epidemics and responses are so varying — we should be working overtime to make use of the time we buy with social distancing. That means:

Building capacity to control transmission by continued social distancing, massive testing, and meeting the needs of healthcare workers for personal protective equipment.

Investing in efforts to mitigate the impact of Covid-19 by rapidly finding treatments, increasing health care capacity, and further accelerating work on a vaccine.

Despite the near-drowning of hospitals and intensive care units we’ve observed in many countries, and may soon witness in the U.S., we must think clearly and understand that getting through the first phase of this pandemic only gets us into the life raft, not to dry land.

Marc Lipsitch is professor of epidemiology and director of the Center for Communicable Disease Dynamics at the Harvard T.H. Chan School of Public Health, where Yonatan Grad is an assistant professor of immunology and infectious diseases.