It added that special populations such as refugees, internally displaced populations, and victims of disasters, constitute potential victims of the listed diseases.
Highlighted in the 2018 annual review of the Blueprint list of priority diseases, WHO said it developed a tool to determine which diseases and pathogens pose a public health risk due to their epidemic potential.
Disease X isn't a recently recognized killer pathogen.
By placing this mystery illness on the "List of Blueprint priority diseases", alongside conditions such as MERS and the Marburg Virus, WHO acknowledges that infectious diseases can happen anytime, and are highly unpredictable.
Along with disease X, the World Health Organization named seven other potential global disease threats, each lacking an effective drug or vaccine. There, it joins #Deadly Diseases such as the Zika virus, Ebola, and SARS (severe acute respiratory syndrome).
Not a great deal is known about the disease yet, although World Health Organization warns that Disease X needed to be included on the list because of its unpredictable nature.
Speaking to The Telegraph, scientific adviser to the World Health Organization and chief executive of the Research Council of Norway, John-Arne Rottingen, said that the next big outbreak is likely to be something not seen before. This is not a newly introduced pathogen and can be caused by a number of biological alterations such as Spanish Flu or Human Immunodeficiency Virus. However, it also warned that these pathogens still pose a serious risk to public health, and should be "watched carefully".
Disease X could also be a zoonose like HIV, salmonella, and Ebola, all of which originated in animals but crossed over the humans in the 19th and 20th century.
"It may seem unusual to be adding an "X" but the point is to make sure we prepare and plan flexibly in terms of vaccines and diagnostic tests".
The power of animal and human contact has ended up to be significantly more prominent as the world develops.
"It's a natural process and it is vital that we are aware and prepare".
Whatever the case may be, the WHO hopes its list will spur governments across the globe to invest more into strengthening local health systems. "It is probably the greatest risk", Mr. Rotingen adds. This new disease is still not made its way into the ecosphere but can be fatal if not treated at the right time.