The second-largest Ebola outbreak in history has spread to a city in the east of the Democratic Republic of Congo, as health experts worry whether stocks of an experimental vaccine will run out.
Butembo, with more than one million residents, is now reporting cases of the deadly haemorrhagic fever. That complicates Ebola containment work already challenged by rebel attacks elsewhere in the DRC that have made tracking the virus almost impossible in some isolated villages.
"We are very concerned by the epidemiological situation in the Butembo area," said John Johnson, project co-ordinator with Doctors Without Borders. New cases are increasing quickly in Butembo's eastern suburbs and outlying, isolated districts, the charity said.
The outbreak declared on August 1 is now second only to the devastating West Africa outbreak that killed more than 11,300 people between 2014 and 2016. There are currently 471 Ebola cases, of which 423 are confirmed, including 225 confirmed deaths, the DRC's health ministry said on Thursday.
Without the teams that vaccinated more than 41,000 people so far, this outbreak could have already seen more than 10,000 Ebola cases, the ministry said.
This is by far the largest use of the promising but still-experimental Ebola vaccine, which is owned by Merck. The company keeps a stockpile of 300,000 doses, and preparing them takes months.
"We are extremely concerned about the size of the vaccine stockpile," the World Health Organisation's emergencies director, Peter Salama said.
Health workers received a dose in a "ring vaccination" approach, but in some cases all residents of hard-to-reach communities were offered it. The prospect of mass vaccination in a major city like Butembo has raised concerns. Dr Salama called this approach "extremely impractical".
This Ebola outbreak is like no other, with attacks by rebel groups halting containment work for days at a time. Some wary locals resisted vaccinations or safe burials of Ebola victims as health workers battle misinformation in a region that has never encountered the virus before.
A "fringe population" has regularly destroyed medical equipment and attacked workers, Health Minister Oly Ilunga Kalenga said last week.
Thousands of people have been organised by Red Cross societies and others to go house-to-house dispelling rumours and checking on possible contacts of victims.
Fatoumata Nafo-Traore, Africa regional director for the International Federation of Red Cross and Red Crescent Societies, joined an awareness campaign in the outbreak's epicentre, Beni, this week.
The head of one family thanked her for the face-to-face contact, saying he did not even have a radio and did not understand what was happening. "Ignorance is the enemy," another resident said.
Given the years of conflict in eastern DRC, it is essential that households trust why the health workers are there, Dr Nafo-Traore said.
Although she called the insecurity "very worrying", she said that with new tools at hand, including vaccines, "there is great hope".