"Until every chain is found and broken, the epidemic will continue and will continue to pose a threat to DRC, its neighbours and the region as a whole," the WHO's director-general, Tedros Adhanom Ghebreyesus, told reporters in Geneva.
The number of deaths in Congo's Ebola outbreak has surpassed 3000, government data showed on Wednesday, as the country's worst epidemic continues to spread across its northeast.
The outbreak, caused by the Bundibugyo species of Ebola, became the largest and deadliest in Congo's history after surpassing the 2018-2020 epidemic.
It is now second only to the 2014-2016 West African outbreak, which infected over 28,600 people and killed more than 11,000 across Guinea, Liberia and Sierra Leone.
But there is now hope of possible progress in treatments and vaccinations. The WHO aims to start clinical efficacy trials of potential vaccines next month or in November, and trials on treatments are under way.
However, Tedros said many deaths were among people who were not on a list of known contacts.
"That means there are chains of transmission we don't know about," he said, adding that many of those who died were still being buried unsafely, which is fuelling transmission.
He urged the international community to increase and accelerate funding for the Congolese government-led Ebola response plan, which is seeking $US1.3 billion ($A1.8 billion).
While the WHO has managed to ship 320 tons of supplies, and has increased testing capacity to 3000 tests per day, it needs further funding to help support its response - including to increase bed capacity at Ebola treatment centres.
Luca Fontana, technical officer for health and technical logistics with the WHO, said it costs $US15 million ($A21 million) per month for a 1500 bed treatment centre.
"We know that we are making this request at a time when financing for humanitarian assistance has contracted," Tedros said. "But as we know from previous Ebola outbreaks, we can control this epidemic if we choose to."
More than 300 Ebola patients have been enrolled for a trial of two treatments, Tedros said.
Trials are also under way of the antiviral drug obeldesivir among people considered high-risk contacts of Ebola cases, to assess if it is effective in preventing disease after exposure to the virus.
Two new vaccines against Bundibugyo virus are in safety trials in Britain and Canada. It is not known whether an approved vaccine against the Zaire Ebola virus would be effective against Bundibugyo virus, so it requires clinical efficacy trials, the WHO said.
"WHO is working with partners to progress all three vaccines to efficacy trials in DRC, starting in October or November," Tedros said.
