LAGOS, Nigeria (AP) — The World Health Organization said Thursday that 31 of 38 confirmed Ebola cases have resulted in deaths in southern Congo, where authorities are battling a new outbreak of the deadly virus.

The latest figures show the casualty rate has nearly doubled since last week — from 16 — and that the disease is spreading rapidly as more than 900 contacts have been identified so far, according to the WHO. Vaccinations began in the affected region on Sunday.

“More than 500 health care workers and contacts have received their vaccination, offering them crucial protection,” said Dr. Patrick Otim, an official at WHO Africa’s program.

A fresh Ebola outbreak was announced by Congolese authorities on Sept. 5 in the locality of Bulape in Kasai, a south-central region in Congo close to Angola.

Last week, the Africa Centers for Disease Control and Prevention said the disease had spread from two districts to four.

An additional batch of vaccines approved by the International Coordinating Group on Vaccine Provision will start arriving from Friday through Sunday, according to Sheillah Nsasiirwe, Health Emergency Officer for Immunization at WHO Africa.

“The vaccination has not been implemented as fast as we would have desired it to because of accessibility challenges which have caused delays in transporting the vaccines,” she said. WHO officials said they have been transporting the vaccines in small batches due to a lack of storage infrastructure in Bulape.