More than 20,000 people could be infected by the current outbreak of the Ebola virus, the World Health Organisation said.
They said the actual number of cases in four West African nations could already be two to four times higher than the reported 3,069, as they issued a strategic plan to combat the outbreak.
They said: "The actual number of cases may be 2-4 fold higher than that currently reported."
They added that their road map "acknowledges that the aggregate case load of Ebola Virus Disease could exceed 20,000 over the course of this emergency."
They said: "Response activities must be adapted in areas of very intense transmission and particular attention must be given to stopping transmission in capital cities and major ports, thereby facilitating the larger response and relief effort."
UK trials of a vaccine for the Ebola virus began today - but some experts complain that the response has been a long time coming.
A Swansea doctor who took leave to treat Ebola patients in Africa, is back on the wards after three weeks in isolation.
The first British case of Ebola in the outbreak in West Africa has been confirmed. So how would repatriation work are what are the risks?