The World Health Organization (WHO) has for the second time this year declared Liberia free of Ebola, a deadly disease that killed thousands in three west African countries since it broke out more than a year ago.

West African nations of Liberia, Guinea and Sierra Leone were ravaged by an outbreak of the Ebola virus that  killed nearly 11,000 people since march 2014, before being contained and a vaccine developed by global drug companies.

Liberia had initially been declared Ebola-free on May 9, but the death of a teen in June  lead to six more cases being discovered in the country. One more person who had contact with the teen died later in July.

The last infected person was tested and cleared for the virus, which has a life cycle of 21 days, over 42 days, over 42 days ago.

“Today the World Health Organization declares Liberia free of Ebola virus transmission in the human population,” Dr. Alex Gasasira, WHO’s representative in Liberia, was quoted by The New York times saying.

Liberia’s Ministry Of Health has said it will maintain “heightened surveillance” around the country for another 90 days before declaring the country Ebola-free. It also urged Liberians to continue observing preventive measures like washing hands.

More than 4,800 people have died in Liberia because of the Ebola crisis, according to WHO data, which also showed that 2,500 people died in Guinea and 3,950 died in Sierra Leone.

The other two countries are still witnessing some cases of Ebola infections and are yet to be given a clean bill of health by WHO.

“WHO commends the government of Liberia and its people on the successful response to this recent re-emergence,” the organization said in a statement. “It is in full accord with government calls for sustained vigilance.”