Centers for Disease Control Director Tom Friedman did not return from his visit to West Africa, where the worst outbreak of Ebola in history has spread to five countries and killed at least 1,500 people, with any good news.

Friedman told CNN hosts on Tuesday that the Ebola outbreak in Africa is currently “completely out of control” and is now an “epidemic.” The CDC director added that “it will get worse in the future and our window of opportunity to turn it around is closing.”

This outbreak has resulted in accelerated research and testing of an experimental Ebola vaccine. Experimenting with a workable vaccine will begin this week at the National Institutes of Health. “According to the NIH, the vaccine will also be tested on healthy volunteers in the United Kingdom, Gambia and Mali, once details are finalized with health officials in those countries,” CNN reported.

But while the West seems largely convinced that superior medical technology and detection methods will prevent the disease from spreading to the United States, two experts on viral outbreaks are not so sure.

Writing in The Wall Street Journal opinion pages, former Food and Drug Administration Deputy Commissioner Scott Gottlieb and former Health and Human Services Deputy Secretary Tevi Troy do not expect the U.S. to escape the consequences of globalization that easily. “Given international travel, we will certainly see cases diagnosed here, and perhaps even experience some isolated clusters of disease,” they write, though noting that a West Africa-style outbreak is highly unlikely in the industrialized world.

They advocated for a major campaign to contain the virus in Africa and to aid those suffering as a result of this historic outbreak. The two experts add that the virus is already mutating fast and will be even more difficult to treat as it continues to evolve.

Could Ebola mutate and become airborne? It would be highly unlikely for a virus to transform in a way that changes its mode of infection. Yet this disease produces a massive level of the Ebola virus in the blood, called viral load, which can lead to excessive mutations. An Aug. 28 article in the journal Science shows that Ebola is already mutating during the current outbreak, in ways that could make it harder to diagnose. So the longer the virus spreads unchecked, the greater the chance of other random mutations that could also make it harder to contain, or to target with a new drug.

The World Health Organization warned last week that, “The Ebola outbreak will affect more than 20,000 people in West Africa and might spread to more countries, indicating a clinical emergency all over the world.”

“It requires worldwide effort costing more than half a billion dollars to overcome the deadly Ebola outbreak,” the group added.