Sitting and talking about the 10,000 people so-far killed by Ebola hemorrhagic fever in West Africa, it's easy to feel impotent. The scope and nature of the problems that fed the outbreak are the result of disparities so vast they border on abstraction. There are fewer doctors in the entirety of the hardest-hit countries than there are on K Street in Washington, D.C. But this morning, at an Atlantic Live event five blocks south of that commercial corridor, the director of the National Institute of Allergy and Infectious Diseases, Anthony Fauci, and I sat and talked—about how this happened, and about the complex psychology inherent to preventing the spread of infectious diseases.

In the case of measles, much more immediately threatening to Americans than Ebola, Fauci said that states could do more to require parents to vaccinate their kids. For one, they can reconsider the "personal belief" exemptions, in which parents can choose not to vaccinate their children based not on any medical condition, but on some ethereal notion that almost always amounts to misunderstanding of the science. He raised the idea of personal freedom, which is really at the core of objections to vaccine requirements. Of course, infants cannot be vaccinated in their first year of life, leaving them susceptible to anything, so choosing not to vaccinate is no more a matter of personal freedom than choosing to drive drunk or practice blindfolded archery in a crowded elevator.  

In a country where parents are willfully exposing their children to the potential for highly contagious, even lethal infections, is it realistic to expect Americans to invest in preventing outbreaks on the other side of the world? The central question is how to get people to care about infectious disease beyond one's own near-term likelihood of contracting something. How do you balance an appropriate level of concern, enough to inspire necessary support for preparedness, without causing panic?

Fauci is presently caring for a man who is in critical condition, hospitalized at the specialized clinical studies unit National Institutes of Health after contracting Ebola during his work in Sierra Leone. There is no cure for the disease, but the odds of surviving are much greater when you're in a place that can keep refilling you with blood and pumping air into your lungs after your body stops doing so on its own.

"This patient, without a doubt, had he [remained] in West Africa, he would be dead now," Fauci said. "There's no doubt about that." In the United States people can at least sometimes be kept alive, if unconscious, as the disease runs its course. Elsewhere it is essentially a death sentence, the notion of which made the virus so scary to many Americans, even as about half of them forewent influenza vaccines last year and more than 100 children died of the flu.

Last week the World Health Organization announced that the Ebola outbreak in West Africa is on pace to end by this summer, with the proper allocation of resources. There have been no new cases in Liberia over the past month, though the virus smolders in Guinea and Sierra Leone. At the risk of conceding that this will indeed end relatively soon, the American conversation has turned retrospective. This morning Bill Gates wrote 2,600 words in The New England Journal of Medicine about what must be done to prepare the world for the next big outbreak: "We must prepare for future epidemics of disease that will spread more effectively than Ebola."

It's a lengthy allocation of space for an esteemed medical journal, unprecedented for a person who is not an academic scientist or physician. But the world has come to rely on philanthropists like Gates to fund relief efforts, because it does not have a well-funded agency in place to control and contain infectious outbreaks before they become crises. Fauci agreed, admitting that the World Health Organization is insufficient in itself, underfunded and decentralized. Director Margaret Chan said as much recently: "[The Ebola epidemic] overwhelmed the capacity of WHO, and it is a crisis that cannot be solved by a single agency or single country."

During the height of Ebola panic in the United States at the end of 2014, the role of officials was largely to quell undue paranoia. Now it has shifted toward acknowledging the ways in which the world is not prepared.

"There are always new diseases that emerge and re-emerge. A new disease that has phenomenal public-health impact doesn't occur very often," said Fauci. "The last major disease that was brand new was HIV/AIDS, recognized in 1981, and since then 37 million people have died." Gates argues that of all the things that could potentially kill more than 10 million people, the most likely is an infectious epidemic—either organic or the result of biowarfare. Fauci puts influenza at the top of that list.

"What we need is an interconnecting global network, of essentially all countries, that can identify [outbreaks], report them, and have a team that can go in and help," said Fauci. "Not every country is prepared to contain an epidemic."

Fauci described Ebola as one of the most devastating diseases a person can have. But it does not compare to measles or influenza in terms of contagiousness. In 1918, the flu killed somewhere between 50 and 100 million people. When I spoke recently with Robert Gallo, director of the Institute of Human Virology at the University of Maryland, he said that the question of whether an outbreak rivaling that scale could happen again is more likely a question of when. The World Bank has estimated that a worldwide influenza epidemic would reduce global wealth by around $3 trillion. In his report today, Gates calls that the cost of inaction.

The cost of action, oppositely, would be a global "warning and response system" that can contain outbreaks before they kill thousands of people. It would mean people caring about investing in health surveillance infrastructure–roads and airports in low-income countries, for example, to get aid workers to the places they are needed, to quickly contain and trace infections. It would mean caring about everyday health systems across the world, especially with an eye to scaling them up when needed.

"The world spends a great deal of money—hundreds of billions of dollars a year—getting ready for war," writes Gates. "I am not saying this is a mistake, but given that an epidemic is more likely to kill millions of people than a future war, I believe we should build on these efforts so we can be more prepared for a severe epidemic."

Gates' case hinges on the idea that if people understand that the cost of inaction is much greater than the cost of action, they will act. It's the same case that Fauci made today for getting parents to vaccinate their kids: "One of the problems in biology is that—unlike mathematics or physics where someone can tell you the exact odds of something happening or not—you never say never, and never say always." But any rational analysis of the extremely rare risks of some adverse reaction to a vaccine leads to a clear choice; one of the clearest of all the interventions that medicine has to offer.

"When patients ask me, 'Is this vaccine 100 percent safe for my child?'" he continued, "well, no, nothing is 100 percent safe. I could've broken my neck walking onto this stage." But the measles vaccine is the most effective vaccine that exists, and it prevents what is one of the most contagious diseases known to science.

So 15 years ago, when the United States declared measles eliminated, Fauci was not imagining sitting and talking about a measles outbreak today. He believes it's ultimately due to the waxing and waning of people's perceptions of risk. When children were dying of measles in the mid-twentieth century, parents jumped at the chance to keep their kids safe. They would likely have done the same in October when they read about the Dallas nurse who got on a plane the night before she developed symptoms of Ebola, were there a vaccine to offer their children. But even just a few months later, with those fears subsiding, would they still?

That's where talking comes in, I suppose. Without being terrifying, keeping people apprised of the risks of complacency. It's a balance that Fauci, after 31 years in his role, strikes well. "A lot of children used to die from measles and polio, things like that, which we don't have right now. So we're, in some respects, the victims of our own success," he said. "We have to continue to realize that the risk of a vaccine is infinitely lower than the risk of the disease itself."

By all accounts, new outbreaks will come. They will come at costs that will be great, but less if the world is adequately prepared.