This is according to the World Health Organization (WHO) said on Wednesday.
The death toll from the outbreak, which has been mostly confined to West Africa, has risen to 7,905, the WHO said, following 317 fatalities recorded since it last issued figures on 24 December.
The number of known cases, including fatalities, totalled 20,206 at year-end, it said.
Sierra Leone accounted for 337 of 476 new laboratory-confirmed cases since 24 December. They included 149 in Freetown, the highest incidence in the capital in four weeks.
The urgent need for assistance in Sierra Leone prompted the United States Agency for International Development to airlift two ambulances to Freetown from Liberia's capital Monrovia, once the worst Ebola hotspot, the United Nations said.
However, the number of cases in Sierra Leone over a three-week period has fallen below 1,000 for the first time since 28 September, suggesting the spread of the disease is slowing. In neighbouring Guinea, the three-week total rose for a second week to 346, suggesting the epidemic is growing there.
(READ MORE: Death toll from Ebola in West Africa rises to 7,518 – WHO)
Nine countries have now reported cases of Ebola. In Britain, a nurse was diagnosed with the virus this week upon her return from Sierra Leone. She is being treated with blood plasma from a survivor of the virus and an experimental antiviral drug, the London hospital treating her said on Wednesday
She had travelled from Sierra Leone to Glasgow via London and did not show symptoms during her journey, although she was "believed to have become febrile around the time of arrival to London", the WHO said.
Ebola broke out for the first time in West Africa a year ago when a two-year-old boy died in southern Guinea on 28 December, but the so-called "index case" only came to light in March by which time the disease had spread widely.
Liberia lifted a curfew imposed to curb the spread of Ebola so that people could attend New Year's Eve church services, as Medecins Sans Frontieres warned of growing complacency over the disease in the country.
(READ MORE: Exhausted Sierra Leone medics battle Ebola in the "Red Zone")
The haemorrhagic fever, which causes vomiting, diarrhoea and bleeding, is spread by contact with bodily fluids. It has no known cure but several major drug makers are developing vaccines already being tested in clinical trials.
The Ebola crisis in West Africa is likely to last until the end of 2015, according to Peter Piot, a London-based scientist who helped to discover the virus in 1976 in the former Zaire, now the Democratic Republic of Congo.