People march with a Liberian flag as they celebrate Liberia being an Ebola free nation in Monrovia, Liberia, Monday, May 11, 2015.
Photo by Abbas Dulleh/AP

Liberia is free of Ebola again, remains on ‘heightened surveillance’

Updated

Liberia’s free of Ebola again, after going 42 days without a case, the World Health Organization said Thursday.

But health officials are wary, because the virus has returned before after apparently having been eliminated.

“Forty-two days have passed since the second negative test on 22 July 2015 of the last laboratory-confirmed case. Liberia now enters a 90-day period of heightened surveillance,” WHO said in a statement.

RELATED: World Health Organization reports progress on Ebola vaccine

“Liberia’s ability to effectively respond to the outbreak of Ebola virus disease is due to intensified vigilance and rapid response by the government and multiple partners,” it added.

“Transmission had been declared over previously on 9 May 2015, but the disease re-emerged on 29 June and 6 additional cases were identified.”

Morning Joe, 7/22/15, 8:49 AM ET

Doctor diagnosed with Ebola on his recovery

This time last year, Dr. Kent Brantly was diagnosed with the deadly Ebola virus while working in Liberia. Dr. Brantly survived, and he joins Morning Joe with his wife, Amber, to discuss his experience, which is chronicled in his new book ‘Called for Life.
More than 28,000 people have been infected and more than 11,000 of them confirmed dead in the epidemic of Ebola that’s lasted well over a year in West Africa.

But officials finally have it almost under control. Just two cases were reported in Guinea last week and one in Sierra Leone. But the case in Sierra Leone was a woman who was only diagnosed after she died — meaning the virus is spreading without being detected. It had been 22 days since the last known case there.

And a baby who died in Guinea also had no known contacts. Officials are trying to figure out how she got infected.

This article first appeared at NBCNews.com

Ebola, Liberia and public health

Liberia is free of Ebola again, remains on 'heightened surveillance'

Updated