With 12 new cases a day, up from 1.3 cases in early September, Ebola is spreading nine times faster now than two months ago in Sierra Leone.
A report by the Africa Governance Initiative (AGI) based on three-day averages of cases recorded by the health ministry comes just after the US ambassador reported encouraging signs of recovery.
"While new cases appear to have slowed in Liberia, Ebola is continuing to spread frighteningly quickly in parts of Sierra Leone," AGI said, reports Al Jazeera. AGI is a support initiative set up by former British prime minister Tony Blair.
Acknowledging the government's measures to control the spread, AGI stressed that the situation was still "a full-blown crisis".
AGI chief executive Nick Thompson said: "But we can't rest until Ebola has nowhere to hide. And we can see from growth in new cases in some rural parts of Sierra Leone that we still have no time to lose if we're going to get on top of this."
Recently, the World Health Organization had stated that Liberia was recovering, based on number of cases and burials reported. It had cautioned against relaxing while noting that containment measures in the three nations will be scaled up by December.
Control measures that include safe burials, contact tracing and better protection for healthcare staff have been emphasised by experts warning against any relaxation.
The disease has claimed over 5,000 lives so far with twice as many, or more, reported and unreported cases according to WHO.