GENEVA – After months of regularly delivering bad news about the Ebola outbreak in West Africa, Dr. Bruce Aylward allowed himself a broad smile Monday.

The news was not uniformly good. New Ebola cases are being reported in western Sierra Leone at an astronomical rate and the contagion there is still out of control. But the epidemic has slowed in Liberia and Guinea, and the World Health Organization is meeting the target it set two months ago of isolating 70 percent of infected people so they can't spread the disease and burying 70 percent of the dead in a way that doesn't further the contagion.

The low-key Aylward declared progress. "This was a very different place 60 days ago," he said.

For Aylward, a Canadian physician and epidemiologist, the heroes of the battle against Ebola are the medical workers who've risked their own health to treat the sick, the political leaders of the countries where the disease rages and the members of the communities who've suffered through the disease.

For many other experts, however, Aylward is a key figure himself, the person who helped turn the tide by working to organize the response in the field.

On Monday, Aylward said there was still much to be done. And progress also brings a risk: that the world will ease up on its push against the disease. "We've reached an important milestone along the way, but that is not going to get you to zero" new cases, Aylward said.

Only at zero can the world be assured that the outbreak has been beaten. And zero, he argued, will come only when 100 percent of the infected people have been isolated and are receiving treatment, when 100 percent of burials are safe and when health workers can trace 100 percent of those who've had contact with sick people.

"The rigor to get to zero will not come through" if the global effort slackens, he said.

Insiders give Aylward, 50, who's written more than 100 peer-reviewed scientific articles and book chapters, credit for providing strategic vision that was lacking for many months after the outbreak was officially reported to the WHO in March.

"Bruce took over like a general," said a health diplomat. Aylward set goals and insisted on results, the diplomat said. "When Bruce took the head seat, things started moving immediately."