Vaccinating against Ebola started on Saturday in Beni, after new cases and the risk of a new outbreak were registered in eastern Democratic Republic of Congo earlier this month.
At least two people died due to the virus in October, only five months since the country declared an end to the last outbreak that killed six people in the region.
Health workers and volunteers visited houses and talked with people in the street, to create awareness and encourage them - especially those who could have been in touch with people affected by the virus - to take the vaccine.
The first case the country registered this month was a child nearly three years-old, sent to the Butsili hospital in Beni after presenting various symptoms related to Ebola. He died on October 6 and tested positive for Ebola, according to the research institute and the health ministry.
About 100 people who may have been exposed have been identified and will be monitored, the ministry said.
According to the World Health Organization, Butsili - a neighbourhood in Beni - was one of the epicentres of the 2018–2020 Ebola outbreak in eastern Congo, considered the second deadliest in the world killing nearly 2,300 people.
The WHO said it's collaborating with the local authorities, adding that it's not "unusual" for sporadic cases to occur following a major outbreak.
Congo has experienced 12 recorded Ebola outbreaks since the virus was first discovered in the conflict-ridden country in 1976.