The World Health Organization’s Africa chief warned on Thursday that the continent now faced a “complex” Ebola outbreak after the virus crossed from east Africa to Nigeria, which has reported the first case in the west of the continent.

“We are facing a more complex outbreak landscape. Nigeria has confirmed an imported case of Ebola virus disease,” Mohamed Janabi, the regional director for WHO in Africa, told an online media briefing.

Nigeria on Tuesday announced an imported case of the Bundibugyo strain behind a major DR Congo outbreak, in a woman, a diplomat who had a history of travel to Uganda.

The case reignited memories of a widespread outbreak in 2014 that struck several countries in the region and killed more than 11,000 people across west Africa between late 2013 and 2016.

Nigeria’s experience in successfully containing the Ebola outbreak in 2014 raised confidence that the country can respond effectively to new public health threats.

The DRC’s Ebola epidemic has become the deadliest in the country’s history, killing 4,381 people out of more than 9,000 confirmed cases since mid-May, according to the health authorities.

A trial of the Ervebo vaccine is underway in eastern Congo. Researchers are hoping to determine if the jab, which is approved for the Zaire strain of the virus, is effective against the Bundibugyo strain driving the current outbreak.

The World Health Organization said in August that 70,000 doses of Ervebo had been approved for use in Congo.

About 50,000 doses are intended for frontline and health workers, while 20,000 doses will be used in a clinical trial to study whether the vaccine protects against Bundibugyo, which currently has no licensed vaccine nor treatment.