KINSHASA (Reuters) – Up to 12 people have been found infected with Ebola in a new outbreak of the deadly disease in the Democratic Republic of Congo, the World Health Organization (WHO) said on Monday.

A week ago, authorities reported six infections in the northwestern city of Mbandaka, saying they appeared to be separate from another outbreak of the virus that has raged in the east since 2018.

There have now been nine confirmed cases and three probable cases of the disease in and around Mbandaka, the WHO said. Six of those people have died, it added.

The city sits on the Congo River, close to the border with the Republic of Congo.

Genetic sequencing of the virus by Congo’s biomedical research laboratory showed the new outbreak is likely to have started as a “spillover event”, a transmission from an infected animal, according to research published on virological.org, a molecular evolution and epidemiology forum.

In a situation report, the WHO said 300 people in Mbandaka and the surrounding Equateur province had been vaccinated – a tool health workers used to control the outbreak in the east, which has not seen any new infections since April 27.

Mbandaka suffered a small Ebola outbreak in 2018 that killed 33 people. Health officials say vaccinations and swift containment efforts including mobile handwashing stations and a door-to-door education campaign kept it at bay.

The new cases in Mbandaka mark the country’s 11th major Ebola outbreak since the virus was discovered near northern Congo’s Ebola River in 1976. It is Congo’s third outbreak in two years of the virus which causes vomiting, diarrhoea and external bleeding.