Damage to most sectors of the economy will see growth shrink from 20.1 percent last year to just five percent in 2014, the finance ministry and the United Nations Development Programme (UNDP) found.
"While priority number one must be to stop the spread of Ebola, protecting Sierra Leone from the wider damage caused by this disease is crucial," said David McLachlan-Karr, the UN chief in Sierra Leone.
"This report is a sobering warning that shows us that Sierra Leone faces a dramatic GDP loss, significant inflation, and a severe drop in trade and production nationwide across many sectors."
It warns that shortages in food and foreign currency, as well as depreciation of the leone, will put further pressure on the recovery.
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Ravaged by an 11-year civil war which left the world with images of child soldiers and rebels funded by "blood diamonds" hacking off limbs, Sierra Leone was long sidestepped by investors.
At the end of the conflict in 2002 some 50,000 people had died, public services were non-existent and the economy was in tatters.
The government launched a three-day shutdown in September to contain the virus and has placed five districts under quarantine, containing almost half the population of six million.
Lockdowns and health checkpoints have limited the movement of food and commodities, causing prices to soar and incomes to shrink, the UNDP said.
Children face at least a year of academic disruptions while expectant women are dying in childbirth at "alarming rates" due to fear of hospitals and a collapsed health service, it warned.