KINSHASA, Congo — Congo’s latest outbreak of the deadly Ebola virus is over, the health ministry announced Tuesday, after a speedy response to limit its spread in remote rural areas and a city of more than 1 million people.

Health experts said the use of a still-experimental vaccine on more than 3,300 people was a major factor in containing the outbreak, Congo’s ninth since the hemorrhagic fever was first identified in 1976.

There were 54 Ebola cases, including 33 deaths, in the outbreak that was declared in early May in northwest Equateur province, the health ministry said.

“Although the scale of the crisis we were facing was unprecedented, the speed and effectiveness of the response put in place by the government and its partners were also exceptional,” Health Minister Dr. Oly Ilunga Kalenga said.

The outbreak posed a serious challenge when it spread to the city of Mbandaka and its more than 1 million residents. The other initial cases were in hard-to-reach rural areas without basic infrastructure such as electricity, making the vaccination efforts more difficult.

“From the start, we had prepared for the worst of scenarios,” the health minister said. “And our fears were quickly confirmed” with the spread to Mbandaka early on in the outbreak.

The city sits on the heavily traveled Congo River upstream from the capital, Kinshasa, and its 10 million residents. There were concerns the virus would spread not only within the country but to neighboring nations including Central African Republic.

The outbreak was declared over after a 42-day observation period, equaling two 21-day incubation periods, with no new confirmed cases recorded.

“It’s a great relief for us,” said Dominique Ekila, a 44-year-old resident of Kinshasa. “Since May, I had stopped traveling to Equateur province to sell fish … With this announcement I will soon plan my next trip.”

Esther Mavinga, who sells vegetables in Kinshasa, said she was grateful the outbreak was over.