A health worker takes the temperatures of U.S. Marines arriving to help combat the Ebola outbreak in Liberia. (John Moore/Getty Images)

Laurie Garrett is a senior fellow for global health at the Council on Foreign Relations. Her latest book is “I Heard the Sirens Scream: How Americans Responded to the 9/11 and Anthrax Attacks.”

The Ebola outbreak in West Africa has reportedly claimed close to 4,000 lives, and World Health Organization officials believe the true death toll could be far higher. An international response — including U.S. military personnel, as well as assistance from several other countries and nongovernmental organizations — has begun, yet global concern about the virus is spreading. How worried should we be? What are the risks? Let’s separate fact from fiction in this crisis.

1. Ebola won’t spread in rich countries.

Until nurse Teresa Romero Ramos contracted Ebola in Madrid, the wealthy countries of Europe, North America and Asia seemed confident that the virus could be contained in advanced medical facilities. As Tom Frieden, director of the U.S. Centers for Disease Control and Prevention, put it after the first U.S. Ebola case was confirmed in Dallas: “We’re stopping it in its tracks in this country.” Such assurances help calm people’s nerves but may be overstated. No system of protection is 100 percent. The Spanish government has concluded that Ramos got infected as she was removing her protective suit, touching her face before disinfecting her hands.

Like Ebola, the SARS virus spreads in hospitals, primarily through physical contact with contaminated fluids. As SARS spread across Asia in 2003, some hospitals, including in Hong Kong, had large numbers of health workers infected, while nearby facilities with similar populations of SARS patients had no employee infections.

The Ebola outbreak in West Africa has reached the United States, as officials confirm one case in Dallas. Here's how U.S. health officials plan to stop the virus. (Gillian Brockell/The Washington Post)

Hubris is the greatest danger in wealthy countries — a sort of smug assumption that advanced technologies and emergency-preparedness plans guarantee that Ebola and other germs will not spread. It was hubris that left Toronto’s top hospitals battling SARS in 2003, long after the virus was conquered in poorer Vietnam. It was hubris that led the World Health Assembly in 2013 to cut the WHO’s outbreak-response budget in favor of more programs to treat cancer and heart disease. And it is hubris that causes politicians to routinely slash public health budgets every time the microbes seem under control, only to cry out in desperation when a new epidemic appears.

2. Post-9/11 emergency preparedness has the United States ready to fight Ebola.

In the years after the attacks of Sept. 11, 2001, and the anthrax mailings to political and military targets, the George W. Bush administration ordered a massive overhaul of bioterrorism preparedness. From the CDC and Defense Department down to rural community clinics, doctors, nurses, hospitals and rapid-response teams went through drills imagining the arrival of pandemics or terrorist bioattacks. Routines were put in place that supposedly prepared every health department in America for the arrival of a highly contagious disease. Military and health agencies were given billions of dollars to create rapid diagnostics, vaccines and cures for highly pathogenic organisms. On every list of biological organisms of concern was Ebola. So it is reasonable to assume that billions of dollars and countless exercises later, the United States is prepared.

But most of the training — both military and civilian — imagined the biological equivalent of an attack, in which something evil is found; responders from police, fire and health departments swoop in wearing hazmat suits; and boom: The infected people are identified, isolated and treated, and the danger to the community is gone. Even in 2005, when the White House feared that a highly virulent pandemic strain of bird flu would sweep across America, preparedness plans focused on isolating a germ and its carriers the way a bomb or chemical weapon might be isolated and defused. Missing was preparation for a long haul of contagious patient treatment, with health workers repeatedly exposed to possible contamination.

Today, in the face of requests for help in West Africa, the answer from the U.S. Agency for International Development is: “There isn’t an existing cadre of people who have experience in treating this epidemic.”

3. It could go airborne.

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Yes, the virus is mutating — a recent paper in Science shows that more than 300 mutations have occurred. But what is now a virus that latches onto receptors outside endothelial cells lining the circulatory system won’t change into one that can attach to the alveolar cells of the lungs. That’s a genetic leap in the realm of science fiction.

Viruses mutate for two reasons: random error and natural selection. Random transformation from a virus solely adapted to infect cells that line blood vessels into one that can attach to entirely different classes of proteins found in the lungs borders on the impossible. Natural selection can overcome the impossible if great pressure is put on a viral population, forcing it to alter or die out. But in Liberia, Sierra Leone and Guinea, there is no such pressure on Ebola: The virus is spreading readily and infecting thousands of people without any need to change into a radically new form.

Far more realistic and perhaps equally worrisome is that the outer coat of the virus — the parts that are recognized by the human immune system and trigger production of antibodies and killer cells that devour viruses — might respond to immune system attack by mutating their outer proteins. If Ebola made such an adaptation, it might mean that people who have survived the disease could be reinfected, and vaccines now in the pipeline could prove ineffective.

4. Travel bans would keep Ebola from spreading in the United States.

The only evidence that any travel ban in the 21st century slowed down viral spread occurred right after the 9/11 attacks, when airports in the eastern United States were shut down for days, and few Americans traveled far from home for several weeks. Possibly as a result, the influenza season was delayed about two weeks in 2001. But the flu eventually came.

Many nations have banned flights from other countries in recent years in hopes of blocking the entry of viruses, including SARS and H1N1 “swine flu.” None of the bans were effective, and the viruses gained entry to populations regardless of what radical measures governments took to keep them out.

The days of Ellis and Angel islands screening out diseases effectively disappeared with the jet age.

5. A vaccine is around the corner.

There are several vaccine candidates in development right now, two of which recently got green lights from a special WHO scientific panel. That go-ahead means the potential vaccines are now being tested on human volunteers. If after a few weeks of such testing the vaccines are shown to cause no undue side effects, the next phase of trials will be carried out, probably in the epidemic countries, to see if the vaccines can protect people from the virus. If it’s obvious in that phase that the vaccine is protecting people from Ebola, the products move to the final, and most difficult, phase — a clinical trial comparing vaccine vs. placebo in hundreds of people, also in the epidemic area.

The No. 1 question I hear privately from vaccine manufacturers regarding Ebola is: How will people dressed like space aliens in their protective gear get terrified, healthy people in Liberia or Sierra Leone to stand still for a poke in the arm?

At best, a vaccine might be ready for final testing by spring 2015 — and that question of trust will still remain.

outlook@washpost.com

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