As a deadly outbreak of Ebola virus spreads in the Democratic Republic of Congo and Uganda, the U.S. Centers for Disease Control and Prevention said on May 17, 2026, that it is transferring “a small number of Americans” who were in Congo and who were exposed to the virus.

Some of these exposures are classified as high-risk, and among them is an American doctor who has been evacuated to Germany, health officials said.

On May 18, the U.S. also announced a ban on people who have recently traveled to Ebola-affected countries from entering the country.

The World Health Organization declared the outbreak to be an international health emergency on May 17. However, the CDC says the risk to the United States remains low.

As an infectious disease scientist who has studied multiple epidemics around the world, I agree that this reassurance is justified. But one key aspect of this outbreak is highly concerning: There is more than one Ebola virus, and this outbreak is caused by one for which the world has no vaccine.

A familiar name, an unfamiliar virus

First identified in 1976, Ebola viruses have caused dozens of outbreaks across Africa.

The group of viruses that cause the disease, called orthoebolaviruses, consists of six known species, but three cause most large outbreaks: Zaire, Sudan and Bundibugyo. The tools the world developed over the past decade – the licensed vaccine Ervebo and monoclonal antibody treatments – were designed against the Zaire species, which is by far the most........

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