WHO says Sierra Leone free of Ebola, will be monitored

WASHINGTON, DC - SEPTEMBER 24: U.S. President Barack Obama meets with members of the Public Health Service Commissioned Corps (PHS CC) after signing a citation awarding the Presidential Unit Citation to PHS CC members in the Oval Office at The White House September 24, 2015 in Washington, D.C. Members of the PHS CC had participated in the Ebola containment efforts in West Africa. (Photo by Rod Lamkey-Pool/Getty Images)

Credit: Pool

Credit: Pool

WASHINGTON, DC - SEPTEMBER 24: U.S. President Barack Obama meets with members of the Public Health Service Commissioned Corps (PHS CC) after signing a citation awarding the Presidential Unit Citation to PHS CC members in the Oval Office at The White House September 24, 2015 in Washington, D.C. Members of the PHS CC had participated in the Ebola containment efforts in West Africa. (Photo by Rod Lamkey-Pool/Getty Images)

Saturday was a significant breakthrough for Sierra Leone in its struggle with Ebola.

World Heath Organzation officials said the country has gone 42 days without a transmission of the virus, which is twice the maxicum incubation period.

The country will be monitored for an additional 90 days now, WHO Sierra Leone Representative Anders Nordstrom said.

The outbreak has claimed almost 4,000 lives, making it the worst in history.

The Associated Press contributed to this report.