The Democratic Republic of Congo on Monday declared the end of an Ebola outbreak that infected 12 people in the eastern province of North Kivu and killed six of them.

The outbreak was contained using Merck’s Ebola vaccine, which was given to more than 1,600 of the patients contacts, and contacts of contacts, the international medical charity Doctors Without Borders (Medicines Sans Frontiers, or MSF) said.

The cases were genetically linked to the 2018-20 Ebola epidemic that killed more than 2,200 people, the second-highest toll recorded in the disease’s history.

The latest flare-up, the DRC’s 12th since the disease was first identified in 1976, emerged on February 3 in the city of Butembo with the death of a woman whose husband had contracted the virus in the previous outbreak.

The virus can remain in certain body fluids, including semen, of a patient who has recovered from the disease, even if they no longer have symptoms of severe illness.

“I am pleased to solemnly declare the end of the 12th epidemic of Ebola virus disease in North Kivu Province,” health minister Jean-Jacques Mbungani said in a statement on Monday.

“Despite the security context and the COVID-19 pandemic, the rapidity and efficiency of the response put in place by the government and its partners made it possible to defeat this pandemic in less than three months,” he said.

The response was often hampered by insecurity caused by armed groups and social unrest limited the movement of health workers, the World Health Organization (WHO) said in a statement.

“Huge credit must be given to the local health workers and the national authorities for their prompt response, tenacity, experience and hard work that brought this outbreak under control,” said Matshidiso Moeti, the WHO regional director for Africa.

“Although the outbreak has ended, we must stay alert for possible resurgence and at the same time use the growing expertise on emergency response to address other health threats the country faces.”

Mbungani urged the population to remain vigilant, and said surveillance teams will continue to work with the local health authorities to watch for any further cases.

A much-feared viral disease that can lead to internal bleeding and organ failure, Ebola killed some 11,000 people in West Africa between 2013 and 2016.

The DRC is also fighting the coronavirus pandemic. The country has reported nearly 30,000 cases and 768 deaths.