A spokesman for the Geneva-based U.N. health agency told Reuters the WHO was working with specialists to conduct an epidemiological investigation “to better understand the extent of the current outbreak” and to establish who is at risk of becoming infected with Ebola. The GAVI global vaccine alliance said on Friday that some 300,000 emergency doses of an Ebola vaccine developed by Merck <MRK.N> could be available in case of a large-scale outbreak, but it would up to the WHO and others to determine “if and when deployment of vaccine into this outbreak is warranted”. The WHO spokesman said “preparations are being accelerated to ensure that vaccine and equipment be available on site” and “appropriate ethical and regulatory authorisation are being sought”. He added that “if pertinent” an immunisation strategy known as ring vaccination would be the recommended approach. Ring vaccination involves tracing all the people who might have been in recent contact with a newly diagnosed Ebola patient and offering them the vaccine. Results of a trial using this technique with the Merck shot in Guinea showed 100 percent protection in those vaccinated immediately. [nL5N1EG4IP] Health officials in Congo are trying to trace 125 people thought to be linked to the cases identified in the remote northeastern province of Bas-Uele province in northeastern Congo near the border with Central African Republic.