'While the mortality rate of this virus is not as high as with some viral hemorrhagic fevers, there are many more cases of Lassa fever, and a great number of survivors are permanently affected by complications -- such as hearing loss -- so this vaccine may have a much broader application.'

Recently, Lassa fever has been imported by travelers to the United States and Europe. The Lassa virus that causes the disease is considered a potential agent of bioterrorism.

Currently, there is no preventive measure available to halt the spread of Lassa fever, other than rodent control in affected areas. The disease is transmitted to humans from rodents that carry the virus.

The research, which was conducted by a team of US and Canadian scientists and is published in the journal PLoS Medicine, eventually could lead to development of a vaccine for human use.

Huge Public Health Threat

Principal investigators Thomas Geisbert of the US Army Medical Research Institute of Infectious Diseases (USAMRIID) and Heinz Feldmann and Steven Jones of the Public Health Agency of Canada (PHAC) developed the vaccine by inserting genetic material from the deadly Lassa virus into a carrier -- a non-pathogenic form of vesicular stomatitis virus, or VSV.

The team then immunized four rhesus macaques with a single dose of the Lassa vaccine, while two monkeys received only the VSV "carrier" virus. Four weeks later, all six animals were experimentally infected with a lethal dose of Lassa virus. The four vaccinated monkeys survived with no signs of clinical illness, while the two control animals died.

"This is the first vaccine platform shown to completely protect nonhuman primates from Lassa virus," said Dr. Geisbert.

"We are hopeful that the VSV strategy, which we have successfully demonstrated for Marburg, Ebola and now Lassa virus, could have utility against other hemorrhagic fevers as well," he added.

"Lassa fever poses a huge public health threat in Western Africa," said Dr. Feldmann of the PHAC.

"While the mortality rate of this virus is not as high as with some viral hemorrhagic fevers, there are many more cases of Lassa fever, and a great number of survivors are permanently affected by complications -- such as hearing loss -- so this vaccine may have a much broader application," he explained.

Significant Leap Forward

Previous attempts to develop Lassa vaccines were partially successful, but none completely protected nonhuman primates against lethal doses of the virus, according to the study's authors. An effective vaccine against the Lassa virus could help to control outbreaks of the disease in Africa and protect healthcare and laboratory workers.

While these early results are promising, further testing will need to be conducted. Some issues that must be resolved before the vaccine can be tested in humans are the safety of the VSV virus, how long the vaccine protects after the shot, and whether it is active against different genetic strains of the Lassa virus.

"The demonstration of an effective vaccine against a hemorrhagic fever virus, such as Lassa, represents a significant leap forward in our hope for safe and efficacious vaccines for the full spectrum of potential biological threats," said Colonel George W. Korch, Jr., USAMRIID commander.

"This is the second time these scientists have worked together for the advancement of public health, which is a testament to their dedication and the value of collaboration across borders," said Canadian Health Minister Ujjal Dosanjh, referring to the scientists' work on Ebola and Marburg.

Carolyn Bennett, Minister of State (Public Health) added, "Relationships like this enhance science and are a credit to the organizations involved."