Lassa fever vaccine gives complete protection

2019-03-02 06:16:06

By Melissa Lee Phillips A new vaccine that completely protects non-human primates against Lassa haemorrhagic fever has been demonstrated. It uses the same technology that researchers recently used to create vaccines for the Ebola and Marburg viruses. “We have a vaccine system here that looks really promising,” says Thomas W Geisbert, at the US Army Medical Research Institute of Infectious Diseases in Maryland. Lassa haemorrhagic fever is endemic to several countries in West Africa and is estimated to infect more than 200,000 people each year, killing a few thousand. That makes it a much bigger public-health problem than Ebola or Marburg, says Susan Fisher-Hoch of the University of Texas at Brownsville, US. Treatment with an anti-viral drug is sometimes effective, but only if given soon after disease onset. The Lassa virus is transmitted to humans from rodents, and people can also pass it to each other. In the past few years, several travellers returning to Europe or the US from Africa have been found to be infected with Lassa, but they have not spread the disease to others. The risk of Lassa fever spreading outside of Africa is probably quite small, says Geisbert, unless the virus mutates into a more transmissible form. But “where it’s endemic, it really matters,” adds Fisher-Hoch. The vaccine trial was led by Geisbert and Steven Jones of the Public Health Agency of Canada in Manitoba. First, they obtained the genetic sequence for the surface glycoprotein that forms Lassa’s outer protective envelope. Then they put this into an altered form of another virus, called vesicular stomatitis virus (VSV), where it was also expressed on the surface. The researchers immunised four macaque monkeys with this Lassa vaccine and injected two control monkeys with their vaccine for Ebola Zaire instead. After 28 days, all six macaques were injected with a lethal dose of Lassa virus. The two control animals developed fever, rash and anorexia, and succumbed to the disease less than two weeks after virus exposure. But the four vaccinated monkeys “showed no clinical evidence of illness at all”, says Geisbert. They developed strong immune responses against Lassa, including both antibody and white blood cell responses, he notes. The Lassa VSV vaccine is a good candidate for use in humans, Geisbert believes. That is because VSV does not cause severe side effects, as do some other virus vehicles, and the vaccine confers protection after only one injection. “This is clearly the vaccine that’s needed for Lassa fever,” says Fisher-Hoch. But she also notes one potential problem, which is that many viruses, including HIV, are being inserted into VSV for use as vaccines. If VSV is used to deliver too many vaccines, it is possible that some people will develop immunity against VSV itself, and the vaccines will no longer work in those populations. Journal reference: Public Library of Science Medicine (vol 2,