Deadly Marburg virus: scientists race to test vaccines in outbreak

Researchers are in a race against time to deploy vaccines and treatments against a deadly virus that has exploded in Rwanda.
As of 30 September, the central African country had recorded 27 cases and 9 deaths caused by Marburg virus, a highly deadly relative of Ebola virus that also causes haemorrhagic fever, with most cases occurring in health-care workers in the country’s capital, Kigali.

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There are no approved therapies or vaccines against Marburg virus. But if the current outbreak continues — most previous outbreaks have been small and quickly contained — health officials and researchers hope to gather valuable data on the safety and potential effectiveness of vaccines and treatments.
On 30 September, the World Health Organization (WHO) in Geneva, Switzerland, hosted a teleconference that, according to a WHO spokesperson, involved Rwandan scientists appointed by the government to run potential trials of vaccines and treatments, and members of the Marburg virus vaccine consortium (MARVAC), a group of companies, non-profit organizations and researchers.
Basic plans for trials were hashed out in the wake of a 2023 Marburg-virus outbreak in Equatorial Guinea that caused 12 deaths among 17 confirmed cases and another 23 fatal probable cases. But no experimental medicines were tested during the outbreak.
Ira Longini, a biostatistician at the University of Florida in Gainesville and a MARVAC member, says that if the Rwandan outbreak continues, the plan is to trial 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 individual.

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A WHO ethics committee previously approved plans for the vaccine trial, as well as one for treatments such as the antiviral drug remdesivir, which was tested against Ebola and COVID-19, and monoclonal antibody treatments that have shown promise in animals. The WHO spokesperson said the next urgent step is for the trials to be approved in Rwanda.
Several Marburg vaccines are at various stages of development. The furthest along is a candidate led by the Sabin Vaccine Institute in Washington DC that uses a modified chimpanzee adenovirus to deliver instructions for cells to make a Marburg-virus protein. A trial involving 40 healthy participants in the United States found the vaccine to be safe and showed that it generated an immune response against the virus in most people1, and a larger trial is under way in Uganda and Kenya.
A spokesperson for Sabin says that the group is working with Rwanda’s government, but did not say how many doses of its vaccine were currently available. In 2023, a WHO advisory committee named the Sabin vaccine as its top candidate for testing during a Marburg virus outbreak.
A similar vaccine that is being developed at the University of Oxford, UK, was also named as a priority for testing during a Marburg outbreak. Teresa Lambe, a vaccinologist at Oxford who is leading the vaccine’s development, says that the vaccine has so far proved safe in the handful of participants who have received it in an ongoing UK trial.
Mark Feinberg, chief executive of the International AIDS Vaccine Initiative in New York City, says there are currently no doses available of the Marburg vaccine his organization is developing — which is similar to an approved Ebola vaccine — but that production is scheduled to start this week.

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“The Rwandan health authorities are exceptionally capable, and I hope that they will be able to rapidly contain this outbreak,” Feinberg adds. “The risk of extension of the outbreak to adjacent countries is not insignificant and the consequences of this could be severe.”
The fact that clinical-trial plans are in place and that other groundwork has been laid increases the odds that Marburg vaccines and treatments will be used in Rwanda, says Nancy Sullivan, a viral immunologist at Boston University in Massachusetts. But it’s likely that data on Marburg vaccines and treatments will be needed from multiple outbreaks before conclusions can be drawn about their effectiveness.
“The idea now is that you just move forward and don’t worry that the outbreak will end before trial enrolment is complete,” Sullivan adds. “It’s just a piece of the overall trial.”