There is certainly reason to celebrate with Beatrice Yardolo, the last known Ebola patient in Liberia. She survived the terrible disease and was released from a hospital last week. Only five months ago, the virus was raging through Monrovia, the Liberian capital, killing thousands, overwhelming the national health system and sparking riots as authorities tried to quarantine entire neighborhoods.

Now, if no new case appears for 42 days, the epidemic will be considered finished in Liberia. This is a testament to international efforts to contain the virus and the work of the Liberian government. But it’s not over yet.

In Sierra Leone and Guinea, a spike in new cases was reported in the last week of February, though it involved far fewer cases than last summer and fall. The latest outbreaks are in areas where residents have been hostile to health workers, often in the confused belief that the workers were spreading the disease. These are also areas where people have often failed to heed warnings against washing the bodies of Ebola victims, a traditional ritual that exposes all participants to infection.

Health authorities warned about difficulties in the struggle to reach zero cases. The leader of the United Nations Missions for Ebola Emergency Response, Ismail Ould Cheikh Ahmed, told a conference on Ebola in Brussels last week that the greatest danger at this stage is complacency and “a certain degree of fatigue.” And even once zero is achieved, which could happen by summer, major tasks remain.

Liberia, Sierra Leone and Guinea will certainly need considerable help in recovering from the economic and psychological damage of the outbreak. The virus infected about 24,000 people and killed at least 9,600.

Ebola demonstrated that oceans are no longer an obstacle to a raging virus. As this outbreak winds down, all involved must ensure that the next germ never gets as far as this one did and that, once zero is reached, Ebola stays at zero.

FROM AN EDITORIAL IN THE NEW YORK TIMES