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A new mRNA vaccine has been developed that may provide long-term protection against the deadliest viruses in the Ebola family – including the Bundibugyo strain currently spreading in Central Africa.

Over 600 people are thought to have been infected with Bundibugyo virus in the Democratic Republic of the Congo and there have been two confirmed cases in Uganda, leading the to declare the outbreak a public health emergency of international concern.

Bundibugyo virus is a member of a group of pathogens known as orthoebolaviruses, which also includes the most common form of Ebola – the Zaire virus – and Sudan virus. All three can cause severe disease in humans.

Until now, Bundibugyo outbreaks have been rare compared with those of the Zaire strain, which infected over 28,000 people between 2014 and 2016. There are two approved vaccines for the Zaire virus, but none for the Bundibugyo or Sudan viruses.

Now, at the Wuhan Institute of Virology in China and his colleagues say they have developed a vaccine that works in mice to protect against all three viruses.

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“The development of a broad-spectrum vaccine has the potential to efficiently mitigate outbreaks caused by multiple orthoebolaviruses,” they write in the new paper presenting the research.

The challenge for scientists trying to produce a vaccine effective for all three of these Ebola-family viruses is that they each carry different compounds, called glycoproteins, that are essential for infection. However, they all share the same nucleoproteins that package the virus’s genetic material.

To build their new vaccine, Yao and his team combined the mRNA encoding the glycoproteins of each virus – as well as the shared nucleoprotein – inside a single lipid nanoparticle, which is a sphere of fat molecules that protects the mRNA vaccine until it can reach the body’s cells.

Mice were then administered the vaccine and monitored for antigen production before being tested with exposure to all three viruses. All immunised animals gained complete protection against infection by the Zaire and Sudan viruses and were conferred “strong” protection from Bundibugyo.

Hamsters exposed to Sudan virus were also afforded complete protection by the vaccine.

The researchers write that the trials demonstrate that they have successfully “developed a breakthrough multivalent broad-spectrum mRNA vaccine that effectively defends against” the Zaire, Sudan and Bundibugyo viruses.

But they also caution that because the vaccine was only tested on rodents, the full complexity of Ebola’s impact on humans isn’t encompassed and “higher-order” animal testing will need to be conducted.

at the University of Texas Medical Branch says he is “glad to see more creative next-generation filovirus [the group of viruses that includes Ebola] vaccines being explored”.

However, he warns that testing in non-human primates is the gold standard for predicting efficacy in humans, and it will be difficult to get approval for a vaccine targeting multiple pathogens.

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“It’s hard enough to get a vaccine approved for a specific virus. Getting to license with a multivalent vaccine has an arguably more complex path to approval,” says Cross.

at Adelaide University in Australia says it is a “promising” preclinical study, but he also says a limitation is that the findings only apply to rodents.

“It is probably too early to give a firm timeframe for clinical use, but moving from this stage to human trials would usually take several years because further animal work – for example in primates – manufacturing development and safety testing are still needed,” he says.