The Ebola outbreak in the Democratic Republic of Congo is expected to get worse in the coming days and week despite the swift dispatch of an experimental vaccine to the affected area, according to a top official at the World Health Organization.

About 52 people have been infected and death estimates have climbed to 39 as of Aug. 11. An additional 48 suspected cases are under investigation. Peter Salama, WHO’s deputy director, said on Twitter that the outbreak “will get worse before it gets better.”