Health researchers and global health agencies are racing to develop three experimental vaccines against a rare strain of Ebola as fears grow that an ongoing outbreak in central Africa could become one of the most serious in recent years.
The disease, driven by the Bundibugyo species of the virus, has already caused nearly 250 deaths, with more than 1,000 suspected cases reported in the Democratic Republic of Congo and additional confirmed infections in neighbouring Uganda.
The International Aids Vaccine Initiative (IAVI) is leading work on one of the vaccines, while the University of Oxford and pharmaceutical company Moderna are also developing separate candidates targeting the same strain. All three efforts are focused on stopping the spread of the Bundibugyo virus, which has no approved vaccine and has only been detected twice before.
There is already a vaccine available for the more common Zaire species of Ebola, but health experts say it is not effective against this outbreak strain. Vaccines for Ebola must be designed specifically for each species of the virus, of which there are six, although only three are known to cause major outbreaks.
Dr Mark Feinberg, head of IAVI, said: "I think this is clearly threatening to be as severe an outbreak as that, if not even worse, and development of a vaccine, and other countermeasures, is clearly a priority."
Concerns have also been raised by medical aid groups on the ground. Médecins Sans Frontières (MSF) described the situation as "deeply alarming" and said it was the first time "so many cases" had been seen so early in an outbreak.
The outbreak has been linked to the Bundibugyo species of Ebola, which spreads in areas where health systems are weak and conflict has limited access to treatment. Officials fear this could allow the virus to spread more quickly than in past outbreaks.
The scale of the current situation is being compared with the 2014–2016 West Africa Ebola outbreak, which infected nearly 29,000 people and led to more than 11,000 deaths.
The IAVI vaccine approach uses a modified harmless virus that carries the Ebola surface protein. Once inside the body, it triggers an immune response that trains the system to recognise and fight the virus in future infections. Early tests in monkeys have shown strong protection, with close to 100% effectiveness.
Dr Feinberg said their early findings are encouraging, but more work is needed before human trials can begin. The current timeline suggests it could take seven to nine months before the vaccine is ready for clinical testing, although efforts are underway to speed up the process.
At the same time, Moderna is using mRNA technology, the same method used during the Covid-19 pandemic, to develop its vaccine candidate. The approach teaches the body to produce a harmless version of the virus’s surface protein so the immune system can learn to respond quickly.
"We will move with urgency and scientific rigor to support the response and help bring a potential vaccine closer to the communities that need it most," said Stéphane Bancel, chief executive officer of Moderna.
The University of Oxford is also working on a vaccine using a similar genetic approach, which delivers instructions to the body to build a key part of the virus so the immune system can prepare to fight it. Officials say this vaccine could be ready for clinical trials in two to three months.
All three vaccine candidates aim to target the same structure on the virus surface, known as the Bundibugyo glycoprotein, although they use different technologies to achieve this immune response. Researchers say these differences could affect how strong the protection is and how many doses may be needed, which will only be confirmed through trials.
Funding for the early-stage research is being provided by the Coalition for Epidemic Preparedness Innovations (CEPI), which says rapid action is essential as the outbreak continues to grow.
"With Bundibugyo virus spreading rapidly and no licensed vaccines, every day counts in the race against this deadly disease," said Dr Richard Hatchett, CEO of CEPI.
The World Health Organization has also warned about the urgency of the situation. Dr Tedros Adhanom Ghebreyesus, the director general of the World Health Organization, said: "A Bundibugyo vaccine could help to control this epidemic and strengthen preparedness for future outbreaks."
Health experts warn that without fast development of effective vaccines and stronger control measures, the outbreak could continue to spread in areas with limited healthcare access.