A vaccine has been developed that protects monkeys from Ebola and Marburg viruses, as reported in Nature Medicine. The breakthrough comes at a time when both viruses are on the rampage in Africa and are considered to be potential agents of bioterrorism.

Ebola and Marburg are closely related viruses that cause haemorrhagic fever — massive internal and external bleeding — and are lethal in up to 90% of infected monkeys and humans.

The authors of the recent report generated a replication-competent vaccine based on attenuated vesicular stomatitis virus (VSV) vectors expressing a glycoprotein from Ebola or Marburg virus. A single intramuscular injection of monkeys induced protective immune responses — both cellular and humoral — against lethal challenges with either virus.

As the authors report, the use of VSV vectors is "particularly attractive because they can be mucosally administered... [and]... VSV infections in humans occur fairly rarely" (Nature Medicine). Moreover, the live vaccine replicates in the recipient for a short time, generating a rapid and strong immune response. Although these are important features, the authors admit that there are still "questions regarding the safety of live attenuated vectors", owing to their potential ability to recombine with other viruses (New Scientist).

Because monkeys suffer almost identical disease to humans, Steven Jones, the primary author of the study, said that "If we can protect them [monkeys] using this vaccine... then this gives us a good deal of confidence that this will work in humans." (Reuters). However, "it will be some time before we can use these vaccines in the field, but it is satisfying to know we are getting closer", said one of Jones's co-authors, Heinz Feldmann (The Guardian).