I believe that what WHO was looking for is the Corona-Virus

The World Health Organisation (WHO) has put scientists and health workers around the globe on alert for a new and potentially deadly pathogen – Disease X. Each year the Geneva-based organisation list diseases that pose a serious risk of sparking a major international public health emergency. In previous years the list has been confined to known killers such as CCHF, Ebola, Lassa fever, MERS, SARS, Nipha, RVF and Zika. This year a ninth mystery pathogen has been added to the watch list for the first time. „History tells us that it is likely the next big outbreak will be something we have not seen before”, said John-Arne Rottingen, scientific adviser to the WHO committee.

Gillian Anderson: The X-Files – F. Emasculata by Rob Bowman, 25.01.1996
telegraph.co.uk, Paul Nuki, Alanna Shaikh, 10.03.2018
who.int, 07.02.2018