GlaxoSmithKline (GSK), the UK's largest pharmaceutical producer, said development of the company's experimental Ebola vaccine candidate is progressing "at an unprecedented rate," with first phase 1 safety trials with the vaccine candidate underway in the USA, UK and Mali.

Additional trials are due to start "in the coming weeks."

Initial data from the phase 1 trials are expected by the end of this year. If these are successful, the next phases of the clinical trial program will begin in early 2015, with the vaccination of thousands of healthcare workers in the three affected countries of Sierra Leone, Guinea and Liberia, GSK said.

The drugmaker also is working with international health authorities stakeholders to determine how and when near term supplies of the Ebola vaccine could be made available for targeted vaccination of additional health care workers and other people at high risk of infection.

A challenge to the drug's use in future mass vaccination campaigns will depend on whether it provides protection against Ebola without causing significant side effects and how quickly large enough quantities can be made.

GSK acquired the Ebola vaccine candidate with its purchase of biotechnology company Okairos for €250 million in May 2013 and has since been working with the US National Institutes of Health to develop it.