The World Health Organization (WHO) announced on Thursday that the latest outbreak of the Ebola virus in Liberia has ended, bringing one of the worst epidemics in the history of the West African region to a close.

The UN agency, however, warned that flare-ups of the disease could still occur in the coming months, making it necessary to continue surveillance and response initiatives in affected areas.

The WHO first declared Liberia to be free of the epidemic in May 2015, but since then, the Ebola virus had been detected in the country in two separate occasions, with the latest case recorded in November of last year.

For a country to be considered to be free of the Ebola virus, it has to go through at least 42 days, or two consecutive 21-day incubation periods, without recording new cases of infection since the last one that tested negative twice.

According to the WHO, all known transmission chains of the virus have been stemmed in West Africa, and that there has been no new case of Ebola infection detected in Guinea, Sierra Leone and Liberia for 42 days.

"So much was needed and so much was accomplished by national authorities, heroic health workers, civil society, local and international organizations and generous partners," Margaret Chan, director-general of the WHO, said.

However, the resurgence of the virus following the first declaration has caused some observers to be wary of potential flare-ups in the future.

The WHO said it anticipates the possibility of detecting new Ebola cases in Guinea, Sierra Leone and Liberia, which is why it considers the three countries to still be at high risk of additional minor outbreaks of the virus.

Evidence has shown that the Ebola virus can seemingly disappear from the bodies of survivors rather quickly, only to remain in the semen of a small fraction of male survivors for as long as a year. In rare occasions, the virus has been transmitted from the male carrier to their intimate partners, the UN agency said.

Chan explained that the next three months after the declaration is the most critical for Guinea, Sierra Leone and Liberia, the three West African countries that were hardest hit by the disease.

The WHO chief said they expect all survivors of the epidemic to clear Ebola from their bodies by the end of 2016.