“Break the chain of transmission” is the phrase mathematical epidemiologist Gerardo Chowell keeps turning over in his head—which makes sense when you consider that every person with Ebola generates as many as two new cases.

“So you can start to visualize in your mind how quickly this virus can spread in the population,” he says.

Chowell, who has been tracking transmission since this summer, says in Sierra Leone, Guinea and Liberia, the growth rate is exponential.

The way to get in front of that awful math, says the World Health Organization’s Dan Epstein, involves a financial kind of math.

“For a United Nations-wide response, we need about $978 million,” he says.

Epstein says that money would cover 3 million protective suits, 1,000 ambulances and new health centers. But to contain this outbreak, says Epstein, what is needed is courage.

“We really need more people. People to treat Ebola patients. People to bury the ones who have died safely,” he says.

Epstein says at least 750 more doctors are needed. That, and the aid, are the numbers needed to make the outbreak math more manageable.