Right now, the math still favors the virus.
Global health officials are looking closely at the "reproduction number," which estimates how many people, on average, will catch the virus from each person stricken with Ebola. The epidemic will begin to decline when that number falls below one. A recent analysis estimated the number at 1.5 to 2.
The number of Ebola cases in West Africa has been doubling about every three weeks. There is little evidence so far that the epidemic is losing momentum.
"The speed at which things are moving on the ground, it's hard for people to get their minds around. People don't understand the concept of exponential growth," said Tom Frieden, director of the U.S. Centers for Disease Control and Prevention. "Exponential growth in the context of three weeks means: 'If I know that X needs to be done, and I work my butt off and get it done in three weeks, it's now half as good as it needs to be.' "
Frieden warned Thursday that without immediate, concerted, bold action, the Ebola virus could become a global calamity on the scale of HIV. He spoke at a gathering of global health officials and government leaders at the World Bank headquarters in Washington. The president of Guinea was at the table, and the presidents of Liberia and Sierra Leone joined by video link. Amid much bureaucratic talk and table-thumping was an emerging theme: The virus is still outpacing the efforts to contain it.
"The situation is worse than it was 12 days ago. It's entrenched in the capitals. Seventy percent of the people [who become infected] are definitely dying from this disease, and it is accelerating in almost all settings," Bruce Aylward, assistant director general of the World Health Organization, told the group.
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