Scientists are trying to test vaccines in an outbreak

Researchers are in a race against time to deliver vaccines and treatments against a deadly virus that has exploded in Rwanda.

As of September 30, the central African country recorded 27 cases and 9 deaths caused by the Marburg virus, an extremely deadly relative of the Ebola virus that also causes hemorrhagic fever. Most of the cases occurred among health care workers in the capital, Kigali.

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There are no approved treatments or vaccines against Marburg virus. But if the current outbreak continues — most of which are small and can be quickly contained — health officials and researchers hope to collect valuable data on the safety and potential effectiveness of vaccines and treatments.

On September 30, the World Health Organization (WHO) held a conference call in Geneva, Switzerland, with Rwandan scientists contracted by the government to conduct potential trials of vaccines and treatments, as well as members of the Marburg Virus Vaccine Consortium (MARVAC), one Business group, nonprofit organizations and researchers, according to a WHO spokesman.

Ring vaccination

Broadbrush plans for trials were drawn up in the wake of a 2023 Marburg virus outbreak in Equatorial Guinea, which caused 12 deaths among 17 confirmed cases and another 23 probable fatal cases. However, no experimental drugs were tested during the outbreak.

Ira Longini, a biostatistician at the University of Florida in Gainesville and a MARVAC member, says that if the outbreak in Rwanda continues, the plan is to test at least one vaccine in a strategy known as ring vaccination. The approach – which showed the effectiveness of an Ebola vaccine in Guinea during the 2014-16 West African outbreak – involves immunizing contacts of an infected person.

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A WHO ethics committee had previously approved plans for the vaccine trial, as well as one for treatments such as the antiviral drug remdesivir, which has been tested against Ebola and COVID-19, and monoclonal antibody treatments that have shown promise in animals. The WHO spokesman said the next urgent step was to approve the trials in Rwanda.

Several Marburg vaccines are in different stages of development. The most advanced candidate, led by the Sabin Vaccine Institute in Washington DC, is using a modified chimpanzee adenovirus to give cells instructions to make a Marburg virus protein. A study of 40 healthy U.S. participants found the vaccine was safe and triggered an immune response against the virus in most people¹and a larger trial is underway in Uganda and Kenya.

A spokesman for Sabin said the group was working with the Rwandan government but did not say how many doses of its vaccine were currently available. In 2023, a WHO advisory committee named the Sabin vaccine the best candidate for testing during a Marburg virus outbreak.

Fast production

A similar vaccine being developed at the University of Oxford, UK, has also been named as a testing priority during a Marburg outbreak. Teresa Lambe, a vaccinologist at Oxford who is leading the development of the Marburg vaccine, says the vaccine has so far proven safe in a handful of participants who have received it in an ongoing British trial.

Mark Feinberg, executive director of the International Aids Vaccine Initiative in New York City, says no doses of the Marburg vaccine developed by his organization — which is similar to an approved Ebola vaccine — are currently available, but production is scheduled to begin this week.

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“The Rwandan health authorities are exceptionally competent and I hope they can quickly contain this outbreak,” Feinberg added. “The risk of the outbreak spreading to neighboring countries is not insignificant and the consequences could be serious.”

The fact that clinical trial plans are in place and other groundwork has been laid increases the likelihood that Marburg vaccines and treatments will be used in Rwanda, says Nancy Sullivan, a viral immunologist at Boston University in Massachusetts. However, it is likely that data on Marburg vaccines and treatments will be needed in multiple outbreaks.

“The idea now is to just keep going and not worry about the outbreak ending,” Sullivan adds. “It’s just part of the overall process.”