The Ebola outbreak that began in the Democratic Republic of Congo in April was declared officially over on Tuesday in what appeared to be twin triumphs for a new vaccine and rapid response.

Just 33 people died, even though the outbreak reached Mbandaka, a river port city of over one million people. At one point, experts had feared the virus might spread throughout Central Africa.

Three years ago, an Ebola outbreak in West Africa cost more than 11,000 lives. Health agencies were slow to respond, and no vaccine was available until it was nearly over.

The last known case in Congo occurred in early June, and the World Health Organization declared the outbreak “largely contained” three weeks later. Declaring it officially over, however, required waiting 42 days — the length of two viral incubation periods.