Health officials say that Guinea is officially free of Ebola, a milestone achievement for the nation that was the original source of a deadly outbreak of the disease about two years ago.

The World Health Organization (WHO), an arm of the United Nations, made the announcement on Tuesday, saying it had been 42 days since test results on the West African nation’s final confirmed Ebola patient came back negative. The WHO said the outbreak that ravaged Guinea and the neighboring nations of Sierra Leone and Liberia, killing thousands of people and sickening scores more, originally began in Gueckedou, Guinea, late in 2013 before spreading.

According to the Centers for Disease Control and Prevention (CDC), the rare-but-often-fatal disease killed 2,536 people in Guinea, the vast majority of people who fell ill with it. The virus also killed 3,955 in Sierra Leone and more than 4,800 in Liberia. In isolated instances, Ebola arrived in seven other nations and killed 15 more people, including one in the United States.

Though the outbreak received widespread coverage from around the globe, 11,300 of the 11,315 Ebola deaths occurred in the three West African nations most severely impacted by the virus. Likewise, CDC data show 28,601 of the 28,637 suspected ebola cases occurred in those nations.

The WHO deemed Sierra Leone free of the disease in November, according to a statement at the time. The WHO had also declared Liberia free of the disease in September, according to the CDC, though three additional cases of the Ebola virus have surfaced in the past few weeks.

The WHO says that Ebola can linger in the bodies of some male survivors for up to one year, making monitoring important. The organization said officials would be on high alert for the next 90 days to ensure any potential new infections are rapidly discovered to prevent transmission.