On Thursday, the World Health Organization declared Liberia Ebola-free for a second time following a brief resurgence of the disease. Liberia was the hardest-hit nation in the largest Ebola epidemic on record. The country accounted for over 4,800 of the 11,300 people killed by the virus since the end of 2013.

In a statement, the WHO said that in May, the outbreak was declared over when no new cases were reported for 42 days, which was twice the usual incubation period for the virus. But later on, six additional cases were reported, including two people who lost their lives.

On Thursday, health officials reiterated that the nation won’t be safe from Ebola until the whole West Africa defeats the virus.

The tests, in neighboring Sierra Leone, confirmed on Saturday that a woman lost her life because of Ebola, within seven days after the last-known patient in the country was discharged from a treatment center.

The WHO said the people who were in touch with the victim have been offered an experimental vaccine that has come up with promising results in trials in neighboring Guinea. The trials have been extended to Sierra Leone. Guinea, from where the epidemic started has reported two more cases last week.

Presently, Liberia has entered into a 90-day period of heightened surveillance. The WHO mentioned that during this time period authorities will be on the lookout for any possible cases.