First Ebola vaccine clinical trials involving humans scheduled for September
Current Ebola outbreak is worst since disease was discovered in 1976
So far there have been more than 1,200 cases and 729 people have died
There is no cure and no vaccine available to treat or prevent the disease
Around four drugs are in the development stage in the U.S.
But researchers say it is difficult to generate funding to progress vaccines
First drug to prevent the vicious virus is two to six years off, scientists say