The World Health Organisation (WHO) has warned that the current Ebola outbreak in the Congo is on course to surpass the deadliest in history, which broke out more than ten years ago, claimed over 11,000 lives, and jolted efforts to develop a vaccine.

The outbreak in eastern Congo, considered the fastest-growing one yet, has killed over 2,000 people out of more than 4,300 cases. The 2014-2016 outbreak had at least 28,000 cases and took about eight months to reach 1,000 deaths.

“At its current pace, it’s on track to eclipse the West African Ebola outbreak of 2014 to 2016,” WHO chief Tedros Adhanom Ghebreyesus told reporters on Wednesday.

The current outbreak was declared on 15 May, but health authorities now say sequencing showed it began months earlier, in February.

Health experts say this is unlike recent Ebola outbreaks because the rare Bundibugyo virus responsible for it has no approved vaccines or treatments, though efforts to address that are underway.