"There are lots of missing deaths in this epidemic," Christopher Dye, WHO's strategy chief, told AFP, estimating that around 5,000 fatalities could be missing from the count.
This assessment, he said, was based on the knowledge that the fatality rate in the epidemic centred in Guinea, Liberia and Sierra Leone stands at about 70 per cent.
But with total reported cases of infections reaching 13,042, that suggests that many of the deaths were going unrecorded.
The UN's health agency has created confusion with its latest figures of Ebola cases and deaths, which have shown shrinking numbers.
More From This Section
The toll provided Wednesday night showed 4,818 deaths, down from 4,951 reported on October 31, while the number of reported cases fell to 13,042 from 13,567.
This does not mean that the epidemic is over or that people have stopped dying from the deadly virus, Dye said, explaining instead that the drop in numbers was linked to a shift in the way WHO uses different databases to calculate the overall numbers.
Up until recently, WHO had used several different databases from each of the affected countries to calculate the overall number of cases and deaths.
The different sources however meant that the numbers did not always progress in a consistent manner, fluctuating according to what data was available from the separate databases.
To avoid the fluctuations, the agency had shifted to only using data from each of the countries' situation reports, based on daily counts of patients and deaths district by district.