Health workers say an experimental vaccine may help to stop the spread of Ebola virus disease in the Democratic Republic of Congo.

The vaccine is called V920. The drug maker Merck has shipped about 8,600 doses of V920 to the northeastern DRC.

The World Health Organization (WHO) reported on Tuesday that the virus has infected over 50 people in the area. It said the Ebola outbreak is responsible for at least 27 deaths.

Experts have warned this outbreak could be as deadly as the one that hit West Africa several years ago.

WHO officials said 33 people were vaccinated against Ebola on Monday in the city of Mbandaka. Most were health workers. Mbandaka is home to more than one million people.

The V920 vaccine has gone through extensive testing, but is still considered experimental.

Benjamin Djoudalbaye is the head of policy and health diplomacy at the Africa Center for Disease Control and Prevention. He told VOA that an effective vaccine is not enough to defeat Ebola.

The V920 vaccine is not designed for a mass vaccination. Instead, individuals who have come in contact with a patient must be identified and given the drug.

Djoudalbaye said, "The difficult part is to properly list down all the contacts and press them in such a way that they (understand they) can benefit from the vaccine and it will stop the spread of the disease."

WHO workers will follow what is being called the "ring vaccination" method: anyone who has or may come into contact with an infected person is vaccinated to contain the threat. This could include family members, funeral workers and health care workers.

So far, V920 has prevented all those vaccinated from getting infected with the virus. In a test done in 2015, none of the 5,837 people who received the vaccine became sick.

A Merck spokesperson said in an email that the company plans to ask for a license on the vaccine in 2019. But it has made V920 available now because of the outbreak in the DRC.

The WHO has requested an additional 8,000 doses. Merck said it is working to act on that request.

On May 18, the East African Community group warned its members that the virus could spread for two reasons: direct flights between East African countries and extensive trade relations.

The WHO, however, has not declared a state of emergency. Travel to and from DRC has not been restricted.

Djoudalbaye says health officials, non-governmental organizations governments learned a lot from the West African Ebola outbreak in 2014 and 2015. One thing they learned was the importance of health services to support a fast reaction to an outbreak.

Part of that effort is the African Center for Disease Control and Prevention, which opened in early 2017.

Djoudalbaye said existing systems and resources have enabled a speedy response in the DRC. He added, "After the declaration of the Ebola outbreak in DR Congo on the eighth (of May), by the tenth, we were on the ground."

V920 is not new. Scientists at the Public Health Agency, in Winnipeg, Canada, invented the vaccine in 2003. The first tests showed promise. Just one shot of the vaccine prevented animals -- macaque monkeys -- exposed to high levels of Ebola from getting sick.

But the drug was never fully developed. Long and costly tests were not done until the worst Ebola outbreak in recorded history happened in 2014 and 2015. By then, the vaccine had been licensed to Merck and its effectiveness in humans had been established.

More than 11,000 people died in the West Africa outbreak. The majority were in Guinea, Liberia and Sierra Leone. Tests of V920 in the outbreak area helped stop the epidemic.

Experts say keeping the virus contained and the number of deaths as low as possible will require ongoing financial support.

I'm Jonathan Evans.

Jonathan Evans adapted this story from VOA News reports. George Grow was the editor.

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epidemic – n. an occurrence in which a disease spreads very quickly and affects a large number of people

resource – n. a supply of something that can be used when it is needed

extensive – adj. large in size or amount; very full or complete

benefit – n. something that produces good or helpful results

license – n. official permission for something

properly – adj. exactly correctly; demonstrating good behavior

outbreak – n. a sudden start or increase of fighting or disease

dose – n. the measured amount of a drug, to be taken at any one time