Residents of the West Point township in Monrovia, Liberia, attend church after a ten-day quarantine was lifted. Daniel Berehulak / The New York Times / Redux

On Tuesday, President Obama said that Ebola was “spiralling” out of control in West Africa and announced that the United States would send a billion dollars and three thousand soldiers to the region, to provide medical and logistical support. Obama said that the risk of economic collapse posed a security threat not just to the region but to the rest of the world, and that, while we could still save countless lives, we would have to act fast. “We can’t dawdle on this one,’’ he said.

But we have dawdled since the beginning of the epidemic. It started in a remote part of the Republic of Guinea in March. Within days, it had spread to Liberia. The fear grew in April, as the epidemic gained momentum, and by May it had crossed into Sierra Leone. In June, as the virus was spreading in urban areas such as Liberia’s capital, Monrovia*, Doctors Without Borders said that it was “out of control.” By the end of July, the disease had moved into Nigeria, the continent’s most populous nation. Today, the dread is spreading even faster and farther than the virus.

“There are two kinds of contagion,” Jim Yong Kim, the president of the World Bank Group, said earlier this week. “One is related to the virus itself and the other is related to the spread of fear about the virus.” Health-care costs and illness from the effects of the disease contribute relatively little to its economic impact, a World Bank report released on Wednesday found. Rather, eighty to ninety per cent of the economic effects are due to the “fear factor,” which shuts down transportation systems, including ports and airports, and keeps people away from their jobs.

We should send every dollar we can to help these countries fight Ebola; there is no moral excuse for anything less than a total commitment. But the investment is not simply about saving the desperate countries of West Africa. Let’s face it: our concerns are a little more self-interested than that. I can’t make it through a day without somebody, including members of my own family, asking me if Ebola is likely to kill us all.

The answer to that question is no. Despite what one might read in the tabloids or see on cable news, the virus is no more likely to “go airborne” today than it ever has been. It is no more likely to become easily passed by a cough or a sneeze than bird flu, or an errant vial of smallpox, or any number of viruses, known or unknown.

Many commentators have noted, with great alarm, that the virus is mutating rapidly. Viruses do that, and in general we should be grateful that they do. Because, while there are exceptions—and, again, Ebola might even turn out to be one of them—a mutating virus almost always becomes weaker as it changes, not stronger. (There is a simple, Darwinian explanation for this phenomenon: a virus cannot survive on its own. It needs to occupy a host, and, like everything else on earth, viruses are programmed to survive. Any virus that kills every cell it inhabits is going to quickly become extinct.)

The reason the epidemic in West Africa threatens to spiral out of control is that it has emerged in areas with almost no health-care systems and bad communications, and that often lack the most rudimentary necessities of life—passable roads and clean water.

This is not a new problem; it was true a year ago and a century ago. Annual per-capita health-care spending in Liberia last year, according to the World Bank, was sixty-five dollars, up from fifty-nine dollars the year before. In Guinea, the figure is thirty-two dollars. Even Nigerians, who are prosperous by comparison, spend less than a hundred dollars per person each year on health care. (The U.S spends about nine thousand dollars per person. Italy, which has health statistics at least as good as ours, spends about thirty-five hundred dollars.)

Ebola is not a mystery disease, and it is not always untreatable. To stop it will require an intense effort to trace all those who have come into contact with infected people. To stop the spread of infectious disease, you have to find all the people who have had close contact with infected individuals and track them—for three weeks, in the case of Ebola. If they get sick, they will needed to be quarantined.

Tracing contacts, though, requires names, phone numbers, addresses, and a trained cadre of public-health officials. Without additional resources, that is too much to ask of the countries now affected by Ebola. There is an even greater obstacle—the genuine and understandable fear of stigma and oppression.

This is not a problem faced only by the world’s poorest nations. In 1988, I sat in an auditorium in Stockholm as Stephen Joseph, who was then the New York City Health Commissioner, addressed the Fifth International Conference on AIDS. It was an explosive period in the history of the epidemic, and Joseph argued, essentially, that there was no more time to dawdle. He said that public-health officials needed to intervene early, and that meant they ought to develop a system for tracing the contacts of those who had become infected with H.I.V. Medically, the suggestion made sense. In a society in which homophobia was rarely concealed, and where discrimination and fear fed each other constantly, the suggestion caused an uproar, and, at least for a while, it was shelved.

There is nothing wrong with acknowledging that we act in the interest of other humans while at the same time protecting the interests of the United States. Perhaps it doesn’t matter why we care, as long as we do. But it is also worth remembering that every expert agrees that Ebola poses little danger to America. If we had sent that money at any other time, and put it to work improving the health-care systems in West Africa, it would no doubt have prevented the worst effects of this epidemic and saved many lives. It would have blunted the impact of other plagues, too—including fear, the most infectious of all.

* An earlier version of this article incorrectly identified the capital of Liberia as Freetown.