Crisis in Congo: The Search for an Effective Ebola Vaccine

Ebola virions
Ebola virions
Since it was first identified in 1976, Ebola has affected several African countries, most recently the Democratic Republic of Congo.

Since it was first identified in 1976, Ebola has affected several African countries, most recently the Democratic Republic of Congo.

Ebola is a type of hemorrhagic fever caused by 1 of 5 different Ebola viruses. Of these, 4 strains can cause severe illness in humans and animals. The fifth, called the Reston virus, has thus far only sickened some animals.1

The disease is extremely infectious because even small amounts of viral particles are sufficient to cause illness. Laboratory experiments on primates have indicated that even a single virion may be enough to catalyze a deadly infection.1 Human to human transmission of the virus occurs via contact with the bodily fluids of an infected person or objects contaminated by an infected person. Humans also can be exposed to the virus through contact with infected animals, such as during food preparation.

Crisis in Congo

In August 2018, the North Kivu province of Congo experienced an outbreak of Ebola. Nearly 300 cases were reported, 186 of which resulted in death.1 Officials from the United States Centers for Disease Control and Prevention reported concern regarding the ability to control or contain the deadly outbreak.1 However, several recent advances in detecting the virus and vaccinating against it offer hope.

In November 2018, the US Food and Drug Administration announced an emergency use authorization for the DPP Ebola Antigen System, a fast, single-use, portable battery-operated fingerstick test to detect Ebola infection. The system analyzes whole blood samples from people exhibiting symptoms of Ebola, or those with other risk factors, such as living in an endemic region or having contact with people who have shown signs of the disease.2

This is the second rapid antigen fingerstick test approved for emergency use, but it is the first to use a portable, battery-operated reader, 2 which allowed for patients to be tested quickly, and outside of laboratory settings. Rapid detection of infection enabled public health officials to identify and isolate infected people before they are able to pass the virus along to others.

Because the symptoms of Ebola—high fever, muscle and abdominal pains, and vomiting—are the same as those of other, more common, diseases such as malaria and cholera, accurate clinical diagnoses can be difficult.3 Current tests can take between several hours and several days to produce results. These traditional molecular tests detect Ebola virus genes in blood using polymerase chain reaction (PCR) testing.3 While accurate, this type of test requires a blood draw, and secure transportation to a laboratory that has a steady supply of electricity, PCR machines, and highly trained lab workers.3 While awaiting PCR test results, patients often are housed together in crowded improvised wards, potentially mixing people who are ill and those who are uninfected.

While not as sensitive as PCR tests, antibody-based tests, such as the DPP Ebola Antigen System, are helpful and cost-effective screening tools in remote villages.3 For example, if healthcare workers screen a representative sample of the population of a small village and find that none of these individuals test positive for Ebola, they can move on to the next village with fair amounts of confidence that such a village is Ebola-free.3

‘Compassionate Use’ of Trial Vaccines

An investigational vaccine called rVSV-ZEBOV has been recommended by the Strategic Advisory Group of Experts on Immunization for use in Ebola outbreaks caused by the Zaire strain of the virus. The vaccine is composed of a vesicular stomatitis virus (VSV), which is an animal virus that causes influenza-like conditions in humans that has been genetically engineered to contain a protein from the Zaire ebolavirus in order to trigger an immune response to the virus.4

This vaccine is not commercially licensed, but is being used in North Kivu under the FDA’s expanded access rules. The rVSV-ZEBOV vaccine was administered to more than 16,000 volunteers involved in several studies in Africa, Europe, and the United States in 2015 and was found to be safe and protective against the Ebola virus.4 Though further research is needed before the vaccine can be licensed, the high mortality rate in North Kivu resulted in the FDA recommending compassionate use of the vaccine, and administration via a “ring vaccination” strategy to induce herd immunity.

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