Ivory Coast began vaccinating health workers against Ebola in the commercial capital Abidjan on Monday after a case of the deadly virus was confirmed over the weekend.

An 18-year-old woman tested positive on Saturday after travelling by bus to Abidjan from neighbouring Guinea. It is Ivory Coast’s first confirmed case of Ebola in 25 years.

About 200 health workers, many from the hospital in Abidjan where the woman was admitted, received shots and the health ministry said it was aiming to vaccinate 2,000 people by Wednesday. The country has 5,000 doses available.

“This is a situation that is under control,” Health Minister Pierre Dimba told reporters. He said the woman was in stable condition and that authorities had identified about 70 people who travelled in the same vehicles as her.

Ebola spreads through contact with the body fluids of symptomatic people. Health officials try to prevent it from spreading by monitoring and vaccinating people who come into contact with confirmed cases.

The WHO has said it is deeply concerned about the virus’ presence in Abidjan, a densely-populated city of more than 4 million. Ebola typically kills about half of those it infects although vaccines and new treatments have proved highly effective in reducing fatality rates.

In Guinea, the health ministry said on Monday that it would begin vaccinating, although it did not say when. Guinea was declared free of Ebola on June 19 after a four-month outbreak in the south killed 12 people.

Authorities believe the woman who tested positive travelled from northern Guinea by bus, passing through the Nzerekore region in the southeast, where the last outbreak began.

She then crossed Guinea’s southern border into Ivory Coast and reached Abidjan several hundred kilometres farther south on Aug. 11. She was hospitalised the next day.

A WHO report said preliminary genetic sequencing showed a close match between her case and the 2014–2016 Ebola outbreaks, which killed a record 11,300 people. That epidemic originated in south eastern Guinea before spreading to Liberia and Sierra Leone.

Last week, Guinea confirmed one death from the Marburg virus, West Africa’s first case of the highly infectious hemorrhagic fever which is similar to Ebola.