( CNN ) The number of new Ebola cases reported in the three worst-hit countries fell to its lowest level since late June , the World Health Organization said Thursday . Guinea , Liberia and Sierra Leone had a combined total of 99 new cases for the week ending January 25 , the WHO said . The total breaks down to 65 in Sierra Leone , 30 in Guinea and four in Liberia . The number of cases continued to fall in Liberia and Sierra Leone , WHO said , but Guinea 's figure rose from 20 confirmed cases in the previous week . The western district of Forecariah -- where the local community has shown high levels of resistance to measures to limit the disease 's spread -- was the worst-affected in Guinea , with half the new cases for the week , the report said . The response to the Ebola epidemic has now moved to a second phase , WHO said , `` as the focus shifts from slowing transmission to ending the epidemic . `` To achieve this goal as quickly as possible , efforts have moved from rapidly building infrastructure to ensuring that capacity for case finding , case management , safe burials , and community engagement is used as effectively as possible . '' There have been more than 22,000 reported confirmed , probable , and suspected cases since the outbreak began , with almost 8,800 known deaths . According to the latest WHO report , children are less susceptible than adults to contracting the virus , which spreads through direct contact with an infected person 's bodily fluids . People aged 15 to 44 are approximately three times more likely to be affected than children aged up to 14 , while adults aged 45 and older are almost four times more likely to be affected than are children . Even as the number of cases drops , scientists around the world continue to study the virus in a bid to understand how it works and help develop more effective vaccines against it . Dr. Anavaj Sakuntabhai , human geneticist at the Pasteur Institute in Paris , is part of a team working to sequence the virus and monitor how it mutates . `` It 's very important for us to follow what happens with the virus sequence , '' he told CNN . While the virus is not that mutated yet , he said , `` It 's important for us to monitor how it changes and see whether it is more contagious or more lethal . '' His team is using samples from blood collected from Guinea and processed by colleagues based in Dakar , Senegal , who 've been working on the Ebola project since April last year . Sakuntabhai 's team has sequenced about 20 samples so far and hopes to do another 100 in the coming weeks , ultimately sequencing several hundred . Many people 's fears have focused on whether the virus could change to become airborne , but it does n't appear to be easy for it to mutate sufficiently to alter the mode of transmission , he said . Sakuntabhai said it was normal for the virus to change and that it 's `` not something to be frightened of at the moment . '' CNN 's Debra Goldschmidt contributed to this report .
Liberia , Liberia and WHO had below 100 new cases for late June . It 's the first time the number has fallen below 100 in late June since late June .