The announcement was made in Freetown by a WHO representative, Anders Nordstrom on November 7.
A country is declared free of Ebola after two 21-days incubation periods (42 days) have passed and the last known case tests negative.
Following the announcement, Sierra Leone commenced it's 90 days enhanced surveillance which will run until 5 February 2016. The surveillance is to ensure a resilient zero as well as detect and respond to any potential Ebola flare ups.
Hopefully, the last country with some cases of Ebola, Guinea will also be free soon.