Four African countries - the Democratic Republic of Congo, Burundi, Ghana and Zambia - have licensed and can now distribute an Ebola vaccine, which the World Heath Organization (WHO) has hailed as a "milestone".Preliminary study results indicate the Ervebo vaccine, manufactured by Merck, has a 97.5% efficacy rate. Data also suggests that vaccinating people who are already infected reduces their chances of dying.DR Congo is currently battling an Ebola outbreak which has killed 2,249 people since August 2018."The approval of the Ebola vaccine by these countries is another milestone in the fight against this unforgiving disease," said WHO Director General Dr Tedros Adhanom Ghebreyesus."Africa has rallied to cement hard-fought progress to keep its people safe from Ebola," he added.