This is according to a study published on Tuesday by researchers at the US Centers for Disease Control and Prevention (CDC).
The top range of the estimate, 1.4 million, assumes that the number of cases, 5,864 according to the count kept by the World Health Organization (WHO), is significantly underreported, and that it is likely that 2.5 times as many cases, or about 15,000, have in fact occurred.
CDC emphasised that the projections, based on an epidemiological model that takes into account how many people each Ebola patient eventually infects as well as other factors, are based on data from late August.
They, therefore, do not account for the recently announced US government Ebola relief effort, which includes sending 3,000 members of the armed forces to the stricken region and training 500 healthcare workers per week.
(READ MORE: Killings in Guinea show mistrust in Africa Ebola fight)
“Extensive, immediate actions – such as those already started – can bring the epidemic to a tipping point to start a rapid decline in cases,” CDC said in a statement.
“A surge now can break the back of the epidemic,” CDC director Thomas Frieden told reporters. “If you get enough people effectively isolated, the epidemic can be stopped,” he said, adding, “I am confident the most dire projections will not come to pass” now that the international community has begun to respond.
Also on Tuesday, experts from the WHO projected that the Ebola outbreak could infect 20,000 people as soon as early November unless rigorous infection control measures are implemented, and might become a constant, endemic disease in the region rather than being completely eradicated.
In contrast, the WHO in late August predicted that the virus could strike 20,000 people by the middle of 2015. The current death toll is at least 2,811 out of the reported 5,864 cases, the UN agency said.
According to the CDC analysis, published in the journal ‘Morbidity and Mortality Weekly Report’, reported cases in Liberia are doubling every 15 to 20 days, while those in Sierra Leone are doubling every 30 to 40 days.
(READ MORE: Sierra Leone capital at standstill as Ebola lockdown begins)
The essence of the CDC analysis is a mathematical model, called EbolaResponse, that allows researchers to see how different actions affect the course of the epidemic.
For instance, it shows that if by late December 70 per cent of Ebola patients have received treatment – or safe burial, if medical efforts fail – thereby slashing transmission rates, the epidemic begins to decrease and eventually end by late January 2015.
The model also projects that every 30-day delay in reaching that 70 per cent tipping point would triple the number of daily cases at the peak of the epidemic.