The Ebola virus disease is a serious illness originating in Africa. During 2014-15, there was an outbreak that mainly affected three west African countries, Guinea, Liberia and Sierra Leone, which resulted in around 28,000 cases and over 11,0010 deaths. The largest known outbreak of Ebola, it was officially declared over in June 2016.

Symptoms of Ebola include: a high temperature; headache; joint and muscle pain; sore throat; and severe muscle weakness. According to the NHS, symptoms start suddenly between two and 21 days after infection.

This can be followed by diarrhoea, vomiting, a rash, stomach pain, and reduced kidney and liver function. The person may then suffer internal bleeding, and can also bleed from the ears, eyes, nose or mouth. It is often fatal. The infection can spread rapidly through contact with a small amount of bodily fluid.

Earlier in the month, an outbreak of Ebola was reported in the Democratic Republic of Congo. Since then, at least 45 cases have been reported, including three health workers, BBC News revealed. At least 26 people are thought to have died in the current outbreak.

Already, the virus has spread from rural areas to the north-western city of Mbandaka, which is a major transport hub on the River Congo. There are now concerns that the outbreak could reach the capital, Kinshasa, however, the World Health Organisation (WHO) said it has "strong reason to believe that the outbreak can be brought under control."

WHO and its partners are now supporting the Government of the Democratic Republic of Congo in carrying out an immunisation campaign with an experimental vaccine in an attempt to halt the spread of the disease.

The vaccine, which has been developed by Merck (NYSE: MRK), known as MSD outside the US and Canada, is not licensed, but proved to be effective when used in limited trials during the west Africa outbreak.

The WHO has sent over 4,000 doses to the DRC, with more on the way. Health care providers and funeral workers have been the first to receive the vaccination. It will then be extended to over 500 people who may have come into contact with those infected with the virus, in an attempt to "ringfence" the outbreak.

While the experimental vaccination campaign has the potential to help with the outbreak, it faces some unique challenges. As with any unlicensed drug, patients must be informed and give their consent before receiving the vaccine. Translators will be required to assist in the communication between health workers and local communities.

What's more, the country's unreliable electricity supplies could cause further obstacles for the campaign, as the vaccine needs to be stored at a temperature of between -60 and -80 C, BBC News explains.

There is also the issue of transportation. Initial stocks will be delivered to Mbandaka city but, as many of the cases have been reported in remote rural areas, the vaccine must then be transported through dense forested areas.

WHO deputy director-general for Emergency Preparedness and Response, Dr Peter Salama, said: "We need to act fact to stop the spread of Ebola by protecting people at risk of being infected with the Ebola virus, identifying and ending all transmission chains and ensuring that all patients have rapid access to safe, high-quality care."

Speaking to the Guardian, an expert in highly communicable infectious diseases at the Boston University School of Medicine, Nahid Bhadelia, who has frontline experience of the 2014 outbreak, warned against complacency, adding: "The vaccine is a powerful tool but you still need other tools. You still need to find the contacts. This outbreak has multiple epicentres that are some distance apart and include a big city... Then you need some kind of infrastructure to follow up."