The suspected death toll from the Ebola outbreak in central Africa rose again Wednesday, as two exposed Americans were arriving in Europe for treatment and the World Health Organization warned a vaccine was still months away.

Subscribe to read this story ad-free

Get unlimited access to ad-free articles and exclusive content.

There are now more than 600 suspected cases and 139 suspected deaths from the virus, mostly in Congo, the head of the World Health Organization said at a news conference.

“We expect those numbers to keep increasing,” WHO Director-General Tedros Adhanom Ghebreyesus said. “We know that the scale of the epidemic in DRC is much larger,” Tedros said, using the acronym for Democratic Republic of Congo.

With two cases and one suspected death in neighboring Uganda, the WHO warned that although the risk of a global pandemic was very low, the threat for countries in the region was severe.

Battling this epidemic will be difficult because it is being caused by a rare strain of Ebola called Bundibugyo, which has no approved vaccine or treatment and a case-fatality rate of between 30% and 50%. The outbreak was also caught late, believed to have started “a couple of months ago,” Anaïs Legand, WHO technical officer for viral and haemorrhagic fevers, said Wednesday.

Furthermore it is centered in an area riven by recent conflict, with cases already detected in Congo’s rebel-held city of Goma, some 230 miles away from the epicenter.

Officials are still scarred by the memory of an outbreak that tore through West Africa between 2013 and 2016, killing more than 11,000 people.

Meanwhile, an American missionary who contracted the virus while treating patients in Congo has been admitted to a specialist hospital in Germany, that country’s health ministry told NBC News on Wednesday.

Dr. Peter Stafford is now at Berlin’s Charité hospital, where he is being treated in an isolation ward in the department of Infectious Diseases and Intensive Care Medicine, the ministry said. He had unknowingly operated on a patient with Ebola before the outbreak was detected, according to leaders of Serge, the Christian missionary group he works for.

In neighboring Czechia, officials said they had been asked by the U.S. to receive and treat another American doctor who had come into contact with an Ebola patient.

Czech Health Minister Adam Vojtěch said on X that the unnamed person was not displaying symptoms and would be transported to his country in a “special transport isolation box.” The person was due to arrive later Wednesday at Prague’s Bulovka Hospital, which has “specialized facilities for highly dangerous infections.”

Although the most common form of Ebola, the Zaire strain, does have an approved vaccine, Bundibugyo has no such countermeasure. Asked about the timeline for developing one, a WHO expert indicated Wednesday this was months away at best.

Vasee Moorthy, the WHO’s senior science and strategy adviser, told the news conference that one vaccine candidate was 6-9 months away from being available for clinical trials.

Another, being developed by the University of Oxford and India’s Serum Institute, was having doses “manufactured as we speak,” he said.

But there was no data from animal testing to support these shots, and so while “it is possible that doses could be available for clinical trial” in 2-3 months, he added, “there is a lot of uncertainty about whether that is a promising candidate.”