The West African nation of Guinea, where the Ebola outbreak began and the only country where it still lingered, has entered an official countdown toward being declared Ebola-free, officials said.

After a three-week-old baby girl being treated in the nation's capital of Conakry tested negative for the virus in two successive tests, the countdown has begun, and if no new cases are reported in the next six weeks — twice the incubation period of the virus — Guinea will be declared officially free of the deadly disease.

It will then join the neighboring countries of Liberia and Sierra Leone as being considered free of the virus, which killed more than 11,000 people since an outbreak began in Guinea in December 2013.

The World Health Organization declared Sierra Leone free of the Ebola virus last week, and Liberia was similarly classified Ebola-free in September.

In Guinea, the three-week-old patient, named Nubia Soumah, contracted the virus from her 25-year-old mother, who died after giving birth.

After treatment at a Doctors Without Borders clinic in Conakry, she has been free of the virus but will remain in the facility for follow-up care given her young age and fragile condition, officials say.

"She could be the last patient of this epidemic," says Laurence Sailly, an emergency coordinator for Doctors Without Borders in Guinea, noting she would be the first baby born to a mother who subsequently died of Ebola to live beyond just a few days.

As the only survivor on an infected mother, Nubia represents an important medical milestone, the medical charity said.

"We are pleased that she has been tested negative, but as she is the first infected baby to have recovered, she will continue to receive specialized medical support before going back home," Sailly says.

Infants and children fared the worst of any age group during the outbreak, WHO officials say.

Her family is from the Forecariah prefecture, close to the Sierra Leone border and the last area in the country to be affected by Ebola cases.

Hopes remain high that Guinea will be declared free of Ebola.

"The government and the communities have worked hard with us to arrive at this result," says Sailly. "We must still remain vigilant for any potential new cases so that our achievements will not be destroyed."