Editor’s Note: Jeffrey Sachs is a professor and director of the Center for Sustainable Development at Columbia University. The opinions expressed in this commentary are those of the author; view more opinion articles on CNN.

CNN  — 

On Tuesday, the White House projected an alarming possibility: Between 100,000 and 240,000 Americans could die from the Covid-19 pandemic, despite the efforts in place to minimize the spread of the disease. Yet these 100,000 to 240,000 deaths are not inevitable. Far from it. As of Thursday night there have been around 5,850 to date in the US, and of the 242,000 active cases, unfortunately several thousand are likely to die. But the US could still keep the death toll well below 100,000. It all depends on our public policy, and especially on our public health system.

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We are now fighting the disease in intensive care units and through lockdowns, but that’s because the US missed the early chance to take sufficient containment measures through testing, isolating, and contact tracing of individual cases. The federal government was grossly unprepared to handle the rapidly spreading infection, and so were the states and cities, which relied heavily on the federal government. The pandemic engulfed the country before governments at all levels recognized the dire emergency. By that time, the public health containment systems were overwhelmed by tens of thousands of confirmed cases, and many times more untested and unconfirmed infections.

Now, our best hope for saving lives and restoring economic activity is to bring the number of active cases back down sharply through the temporary lockdowns across the nation while rapidly building our public health containment system for the post-lockdown phase.

If lockdowns are able to prevent further viral spread, and they should be able to do so if properly enforced and managed– which is not yet the case in many parts of the country – the number of active cases will fall sharply, mostly through recoveries but also through tragic deaths. But when the infection rate drops, and the economy as well as our daily lives are enabled to gradually restart, we will need to contain the infectious cases that will remain in circulation, so as not to allow the pandemic to resurge.

The spread of the pandemic can be understood using a simple numerical example. The numbers in this illustration are not precise, as they will vary place to place and as there is still much that is not known about the spread of the disease.

Let’s call today day one. Suppose an individual, we’ll call him Jack, becomes infected through contact with a person who caught the virus a few days earlier. Jack becomes infectious to others on day four, but without symptoms appearing on that day. The symptoms, such as coughing, difficulty breathing and fever, begin on day five and Jack remains infectious and in the community through day nine. At that point most individuals recover or at least become much less infectious to others. The unlucky ones end up in hospital and in the most severe cases, die. Such numbers will vary by case, but are broadly in line with the timeline laid out in current studies.

During days four through nine, Jack circulates in the community, especially if his symptoms are on the mild side, potentially passing the infection to others. Let us say that he makes on average 16 daily contacts with others, some briefer, some longer. Most of those contacts don’t infect the other person, but every once in a while the contact does infect the other person, at work, in the theater, across the dining room table, or in some other place.

Jack is infectious to others for six days (during days four to nine), during which he makes 96 contacts in total, and infects 2.4 other individuals (the reproductive number, or the number of secondary infections generated from one infected person, of the novel coronavirus – is thought to be between two and 2.6, according to models from Imperial College). In this scenario, that comes out to about 40 contacts for every one infection, again a rough number broadly consistent with the evidence about the rate of disease transmission.