GENEVA, May 21 (Xinhua) -- The World Health Organization (WHO) said Monday that Ebola vaccination for high risk populations had started in the Democratic Republic of Congo (DRC), which would be key to controlling the current outbreak in the country.

The vaccination is first targeting health workers operating in affected areas, and community outreach has started to prepare for the ring vaccination. The WHO said more than 7,500 doses of rVSV-ZEBOV Ebola vaccine have been deployed to the DRC for vaccination in the northwestern Equator Province, where 46 suspected, probable and confirmed Ebola cases and 26 deaths have been reported as of Friday.

"Vaccination will be key to controlling this outbreak," said WHO Director-General Dr. Tedros Adhanom Ghebreyesus. "We are grateful for the support of our partners in making this possible."

A ring vaccination strategy is used to trace all the contacts and contacts of contacts of a recently confirmed case as soon as possible. Teams on the ground have stepped up the active search and follow up of all contacts. More than 600 have been identified to date.

The vaccine was shown to be highly protective against Ebola in a major trial in 2015 in Guinea. Among the 5,837 people who received the vaccine, no Ebola cases were recorded nine days or more after vaccination.

While the vaccine is awaiting review by relevant regulatory authorities, the WHO has recommended the use of the rVSV-ZEBOV Ebola vaccine under an expanded access/compassionate use protocol during Ebola outbreaks linked to the Zaire strain such as the one ongoing in the DRC.

However, given the remote location and limited road access to the populations affected in the current outbreak in the DRC, implementing ring vaccination and maintaining the required -80 degrees Celsius cold chain presents major logistical challenges on the ground.

The WHO has sent special vaccine carriers, which can maintain the sub-zero temperatures for up to a week, and has set up freezers to store the vaccines in Mbandaka and Bikoro, the major infected areas in the DRC.

The use of the investigational rVSV-ZEBOV vaccine in the DRC marks a milestone for the control of Ebola virus outbreaks, the WHO said, but it's just one of several outbreak control measures, which also include case finding, contact tracing, isolation of suspected cases, prompt laboratory diagnosis, infection control in routine healthcare facilities, safe and dignified burials, community mobilization, and effective response coordination.