Three new vaccines are being developed to tackle the rare species of Ebola that has already killed nearly 250 people.

The International Aids Vaccine Initiative (IAVI), which is working on one vaccine, said the outbreak was threatening to be the worst ever.

The University of Oxford and the pharma company Moderna are also researching vaccines against the Bundibugyo species.

The Coalition for Epidemic Preparedness Innovations (Cepi), which is providing funding to each group, said "every day counts".

There are now more than 1,000 suspected cases in the DR Congo with nine confirmed cases in neighbouring Uganda.

There is growing concern this outbreak – which was detected only after it had spread in a conflict zone with limited healthcare resources – could reach the size of the largest ever Ebola outbreak in West Africa in 2014-16. Then, nearly 29,000 people were infected and more than 11,000 died.

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."

It echoes concerns from the medical charity Médecins Sans Frontières (MSF) which said the situation was "deeply alarming" and never before had "so many cases" been recorded so soon.

Vaccines must be developed for each individual species of Ebola – there are six, but only three are known to cause outbreaks.

There is a vaccine for the most common Zaire species, but this outbreak is being caused by another species, called Bundibugyo. It has only been seen twice before and there is no approved vaccine.

IAVI is working on a modified version of the Zaire Ebola vaccine to fight Bundibugyo. The experimental jab has been tested in monkeys where it rapidly trained the immune system and gave close to 100% protection.

Feinberg said their evidence so far meant he was "optimistic about the potential", but currently it would take seven to nine months to get the vaccine ready for clinical trials - although they are trying to "accelerate those timelines".

Meanwhile, the pharmaceutical company Moderna has announced it is using its mRNA technology – which was deployed to rapidly develop vaccines in the Covid pandemic – to work on Bundibugyo.

"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.

And the University of Oxford has already said it is working on its own vaccine technology, which also saved lives in Covid, to develop a fresh Ebola vaccine.

This should be ready for clinical trials in two to three months.

Each vaccine aims to train the body to spot the same structure on the surface of the virus – known as the Bundibugyo glycoprotein. However, each uses a different technology to get there.

IAVI uses a live, but harmless virus that has been engineered so it also has the Ebola glycoprotein. The immune system fights off the harmless virus and learns to fight Ebola in the process.

The mRNA vaccine and the Oxford vaccine both deliver a snippet of genetic code into the body. Once inside it orders the construction of the Bundibugyo glycoprotein, which the body recognises as foreign and starts to attack.

All would mean that the immune system has a head start when it comes to fighting a real Ebola infection.

However, differences in the technologies and the way they train the immune system could affect levels of protection or the number of doses needed. All this needs to be tested in clinical trials.

Cepi is funding the early stages of research.

"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.

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."