The first batch of an experimental vaccine against the deadly Ebola virus is expected to arrive in Monrovia Liberia on Friday.
The shipment will be the first potentially preventative medicine to reach one of the hardest hit countries.
The 300 doses of vaccine is produced by British company GlaxoSmithKline (GSK) and the US National Institutes of Health.
About 30,000 volunteers including frontline health workers are expected to be experimented.
A version of the vaccine has already been tested on 200 healthy volunteers across the UK, US, Switzerland and Mali.
GSK says it has been found to have an acceptable safety profile so far.
Meanwhile some expert says that, with Ebola cases falling, it may be difficult to establish whether the vaccine offers any protection against the virus.
But it is only in affected countries that experts can determine whether it provides adequate protection against the virus.