AN EXPERIMENTAL vaccine against the deadly Ebola virus could be tested on people in as little as 18 months. The project has been fast-tracked because of the increased fear of bioterrorism after 11 September.
鈥淲e鈥檙e concerned about all the haemorrhagic viruses,鈥� says Gary Nabel, director of the Vaccine Research Center near Washington DC and head of the vaccine programme. 鈥淲e know these viruses have been studied as potential weapons of bioterrorism.鈥�
The vaccine is being developed for American medical, military and peacekeeping personnel, but the researchers hope it will also be made available to people in central African countries, where there have been repeated small outbreaks of the disease. Just this year, 53 out of 65 people infected died in an Ebola outbreak in Gabon. A vaccine could also be crucial in the event of a wider epidemic.
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Ebola poses a serious challenge to vaccine makers because it is so dangerous. Victims die of massive internal bleeding and diarrhoea, and the disease is easily transmitted by body fluids. Creating conventional vaccines made of weakened or inactivated viruses isn鈥檛 safe, because of the risk of some virulent virus remaining in any vaccine. Instead, Nabel made a DNA vaccine consisting solely of the genes for the protein coat of the virus.
The vaccine comes in two shots. First, recipients receive jabs of naked DNA, which stimulates the so-called T cell immune response. Next, the same genes are delivered in a harmless adenovirus, triggering antibody production, the other main kind of immune response.
The prototype vaccine passed initial tests in monkeys with flying colours. But there are safety issues about using adenoviruses, and getting as far as human tests could have taken many years. Now, however, extra funding made available since 11 September has allowed a deal to be struck with Crucell, a Dutch biotech company that already has an approved system for making engineered adenoviruses in bulk for use in humans.
So far, the DNA vaccine has only been tested against the Zaire strain, one of the three known lethal strains of Ebola. 鈥淏ut I鈥檓 optimistic it will work with the others as well,鈥� says Nabel. The vaccine consists of a mixture of genes for the glycoprotein coat of all three strains, he says.
While bioterrorists crazy enough to use Ebola would obviously resort to one of the known strains, experts caution that there may well be others lurking in the wild. The disease was only discovered in 1976, they point out, and its source is still unknown.
Nabel expects to test the vaccine first on healthy volunteers in the US, then on healthcare workers in areas liable to outbreaks. He hopes to try the vaccine in real outbreaks, though it usually takes months for an outbreak in a remote area to come to light, by which time it鈥檚 often too late to vaccinate.