A new medical study has warned an outbreak of Ebola could be twice as big as is currently understood.
The World Health Organisation (WHO) confirmed there were nearly 600 cases and 139 deaths in remote, hard to reach parts of the north east of the Democratic Republic of Congo.
However, a new study by Imperial College London warned there could be up to 1,700 cases.
The central figure was reckoned to be between 400 to 800 cases.
The authors of the report said: "Both methods yield broadly consistent results, suggesting that as of May 17, 2026, approximately 400 to 800 cases of BVD may have occurred in the Democratic Republic of the Congo."
"However, there is considerable uncertainty around these estimates, with values of over 1,000 not being able to be excluded given current data.
Chair of the Board of the Coalition for Epidemic Preparedness Innovations (CEPI) Jane Halton said: "I have described this outbreak as being like an iceberg, we've seen the top of the iceberg, the top, as we get closer to it, is pretty large.
"We are now into the many hundreds of cases and hundreds of deaths, but the truth of the matter is that real numbers are much bigger than that."
The Democratic Republic of Congo has been hit with an outbreak
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CEPI, which funds development of new vaccines and is looking at potential candidates for Ebola, has set the goal of having a safe, effective vaccine for major outbreaks within 100 days.
Unlike with the more common Zaire strain of Ebola, there are no approved virus-specific therapeutics or vaccine for the Bundibugyo strain, which has previously proved less lethal.
World Health Organization (WHO) Director-General Tedros Adhanom Ghebreyesus declared the outbreak of this particular strain of the virus a public health emergency of international concern on Saturday.
He said: "I'm deeply concerned about the scale and speed of the epidemic."
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Red Cross workers have been deployed across central Africa
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Dr Vasee Moorthy, of the WHO’s research and development division, said there were two vaccine candidates, however neither were ready for use.
Dr Moorthy said: "There is a RVSV Bundibugyo vaccine...[but] there are no doses of this which are currently available for clinical trial...The information that we have is that this is likely to take six to nine months."
WHO's representative in DRC, Anne Ancia, said identifying cases was slowed by limited diagnostic capacity for the Bundibugyo strain, with just six tests possible per hour.
Experts say the delays in detecting the outbreak show gaps in preparedness following cutbacks by the US and other major donors to global health funding.
Marco Rubio pledged US support to deal with the outbreak
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US Secretary of State Marco Rubio told reporters in Washington that he was worried about the Ebola situation and that US funds would help open 50 clinics to treat Ebola cases.
Mr Rubio said: "It's a little tough to get to it because it's in a rural area...but we'll have more to announce on that. We're going to lean into it pretty heavy."
President Donald Trump formally withdrew the US from the WHO in January after criticising its handling of the COVID-19 pandemic.
Ms Ancia said the WHO had been working "very well" with the US government on the Ebola outbreak but reductions in health funding had had a "tremendous impact" on the organization's ability to counter the disease.
Warnings have been issued about the new strain
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Director of WHO Health Emergencies Programme Dr Chikwe Ihekweazu said: "This principle of identifying the chains of transmission is the same principle with every Ebola outbreak, and it’s very important to get that right...because that will then enable us to really define the scale of the outbreak.
"We can’t do this without prioritising the community...we have to make that work."