Ebola transmissions over in Liberia, enters 90-day watch

The World Health Organization declared Liberia Ebola-free for a second time on Thursday after the country hardest hit by the deadly virus saw a brief resurgence of cases not long after the first time it thought the disease was gone for good.

More than 4,800 people have died in Liberia since the outbreak began in West Africa in late 2013. The country celebrated what it thought was the end of Ebola in May, but then six more cases emerged the following month.

That started the clock over — 42 days or two incubation periods of 21 days — before Liberia could return to being free of transmission. On Thursday, officials announced they had made it without any more cases.

"Today is a day to celebrate, but we must not forget what we have learned," Chief Medical Officer Francis Kateh said. "As long as there is one person with Ebola in our region, Ebola is a threat."

Sierra Leone made it to 42 days only to have a new case emerge. Guinea, where the epidemic began, reported two new cases last week. Experts have said that frequent travel between the countries contributed to Ebola's spread. Health checkpoints were later put in place that test travelers for high fever — the main symptom of Ebola.

Liberia now enters a 90-day intensive surveillance period, when health care workers are to still be on the lookout for any possible Ebola cases.

The worst Ebola outbreak in history has killed more than 11,300 people overall, hitting primarily Guinea, Sierra Leone and Liberia.