WASHINGTON - The United States and Sierra Leone on Tuesday began enrolling and vaccinating volunteers in the West African country for a candidate Ebola vaccine trial, the US Centers for Disease Control and Prevention (CDC) said.

The trail, to be conducted in the heavily affected areas in the past few months such as the capital Freetown, will enroll about 6, 000 health and other frontline workers to assess the safety and efficacy of the rVSV-ZEBOV candidate Ebola vaccine.

"We hope this vaccine will be proven effective," CDC Director Tom Frieden said in a statement.

Mohamed Samai, acting Provost of the Sierra Leone College of Medicine and Allied Health Sciences and the study's principal investigator, said that his agency is happy to be partnering with the Sierra Leone Ministry of Health and Sanitation and US CDC on this important study.

The trial "may help to prevent future cases of Ebola," said Samai. "It brings me hope and pride that my country can take from this devastating epidemic something that may benefit people around the world."

When participants enroll in the study, they will be assigned randomly to one of two time frames for vaccination, either immediately or about six months later. All study participants will receive the vaccine and be followed closely for six months.

The rVSV-ZEBOV candidate vaccine, developed by the Public Health Agency of Canada and licensed to US company NewLink Genetics, has been studied in over 800 people in Africa, Canada, Europe and the United States.

Early results showed an acceptable safety profile and indicated that the rVSV-ZEBOV candidate vaccine produces an immune response.

At this time, clinical trials for several candidate Ebola vaccines are in various phases, but no vaccines have been licensed for use in humans.