According to an email obtained by the Associated Press, the WHO's anti-coronavirus measures have not been enough to stop the spread of the virus among its staff.
It comes as new restrictions are implemented across Europe, including a fresh lockdown in France.
Hans Kluge told an emergency meeting that the health workforce was as big a problem now as a lack of ventilators and personal protective equipment was in March.
Consistent efforts to increase air quality over the last 20 years are paying off.
Eastern Congo has also marked an official end to the second-deadliest Ebola outbreak in history