THE WORST-CASE scenarios for the Ebola outbreak in West Africa must not be ignored, even if they strain belief. Everything about this epidemic has been worst-case — the scope, the toll, the response. The Centers for Disease Control and Prevention published projections Tuesday with an upper range of 550,000 to 1.4 million cases by the end of January. The World Health Organization, which earlier estimated 20,000 cases overall, now predicts that number will be reached by early November.

A profoundly sobering note of caution was contained in a report by the WHO Ebola Response Team, published in the New England Journal of Medicine. Given the rapid acceleration of infections, the team warned that Ebola may not be contained or burn itself out, as many experts had hoped. Rather, there is a possibility it “will become endemic among the human population of West Africa, a prospect that has never previously been contemplated.” With a case fatality rate of 70 percent, that could mean a long period of death and illness among urban populations of millions.

Good public health practices — locating and isolating the sick, containing the virus with cordons to stop the chain of transmission — are still the basic weapons against a disease for which there is no cure, vaccine or therapeutic. But as the WHO warns, the traditional approach may fail. If that happens, vaccines and therapeutics will become essential. Unfortunately, not a single drug or vaccine is ready.

Drug development is expensive and complex. In the United States, much of the biomedical basic research is supported by the government, but the development of new drugs largely occurs in the private sector, driven by the market. Until this year, there was no market for Ebola virus treatments because earlier outbreaks were all relatively small. Although there are some experimental therapies against Ebola, none have developed very far. Some of these investigational compounds exist only because of extensive investment of the U.S. government in biodefense preparedness over the past 14 years. The worry was Ebola could be used as a bioterrorism weapon; now Mother Nature seems to have pulled the trigger instead.

Intense development work on experimental drugs and vaccines is underway in the United States and United Kingdom, but it is not simple to create a new treatment, put it through clinical trials and manufacture it. Sensitive ethical and logistical questions surround these new remedies, especially if there is a limited supply. Although the need is urgent, rigorous testing for safety and efficacy cannot be short-circuited. But the government, researchers and the private sector must make the quest for therapeutics and vaccines a high priority in case the worst-case scenarios come true.