I just read the Excel model that you can download as part of the article:

- It uses the parameters of previous Ebola outbreaks as a base.
    These outbreaks happened in remote and sparsely populated regions. In contrast, the outbreak in Monrovia has hit slum like neighborhoods. This is a completely different base.

- The Excel model uses a "flat" model of population that doesn't take into account geographical distribution.
    Infectiousness in slums will be a lot higher than in previous outbreaks because of the density of population.

- The model talks about keeping 70% of the infected population at home or in hospitals in order to reduce the infection rate. This way, the epidemic will slowly decrease.
    However, there is widespread fear of hospitalization and the mortality rate of Ebola (80%) basically means that people will distrust any doctors, hospital etc. So I can't see how this should happen.

- In the history of Ebola there was no outbreak of this size.
    In the past there were plenty (relatively) of workers per case. But now patients will outnumber the helpers.

Summary: I can't see why the exponential development could be slowed down as indicated in the model...

The death toll of the disease is 80% of all persons infected.
While the disease increases exponentially, the ratio of infected / dead is around 55% currently. But that still means that 80% will be dead three weeks later.
Source: http://healthmap.org/site/dise...

There are only 4M inhabitants in Liberia, so 1.5M means half of them dead. There will be "unusual effects" of such a situation, namely that everybody will run for their life to get out of the country (and into the neighbor countries). I'd be interested if this is included in the simulation.

Reading the last publications about the spreading of Ebola, I've got the idea that WHO tries to hide information, in particular about the different types of spreading. So I'm making this up from common sense, maybe somebody with access to privileged information might add details:

Spreading in slums: That seems to be the case in Monrovia ultimately. Inhabitants don't trust the public health system (with certain reason...) and believe in which doctors or conspiracy theories. Once >500 persons are infected, it becomes practically impossible to research the infection tree and to isolate contacts. In the last 3 weeks Ebola spread exponentially. Please tell me if I'm wrong, but I got the impression that Monrovia is probably "lost".

Spreading across the "pepper coast" via land connections: The area from Guinea to Ghana seems to be relatively sparsely populated with exception of a few cities. And these cities are now basically disconnected from international air traffic. Part of the borders are closed. The villagers along the land connections will become increasingly suspicious of travelers from the cities, so I would predict increasingly violent confrontations. Maybe this might lead to slower spreading (apart from disastrous consequences for the economy, obviously).

Spreading to Nigeria: Nigeria has 170M population, as opposed to 4M for Liberia, and Nigeria is well connected internationally. The recent cases seem to have been contained and tertiary and quartiary contacts have been followed-up. So apparently things work out better in Nigeria compared to Liberia.

So my understanding is: A Pandemic will start once Ebola reaches the slums of Nigeria and starts spreading to more cases than the MSF or others can contain (maybe some 200-500 cases). The pandemic will end once a vaccine becomes available in large quantities, which is supposed to happen in 3-9 months.

Don't be a victim. Learn the rule. Read "MBA for Dummies" :-)