Disease X refers to an unknown pathogen that could cause a future epidemic or pandemic. The World Health Organization (WHO) coined the term Disease X in 2018 to represent an unknown virus or bacteria that could emerge and spread globally. The WHO said they added Disease X to its list of priority diseases to ensure that research efforts and preparedness plans are flexible enough to respond to unknown pathogens.
According to WHO, the rationale behind Disease X is that history has shown us that major epidemics and pandemics have often been caused by pathogens that we did not anticipate. The WHO says they wanted to raise awareness of the threat of “known unknowns” – diseases that we know could emerge but have not yet. By including Disease X on its list, the WHO hopes to spur research into broad platforms that can respond to a wide range of potential pathogens.
The WHO describes Disease X as “a serious international epidemic that could be caused by a pathogen currently unknown to cause human disease”. It represents the knowledge that the next major outbreak may come from a virus very different from ones we are familiar with, like Ebola, Zika or SARS.
Some experts believe that Disease X will likely originate from an animal virus that spills over into humans, known as a zoonotic transmission. Others have speculated that a synthetic virus or bioweapon could also potentially cause Disease X. However, the WHO has said it is unlikely that Disease X would originate from a synthetic virus.
In early 2020, the new coronavirus disease COVID-19 emerged and some experts described it as the first incarnation of Disease X – an unknown pathogen that sparked a global pandemic. The COVID-19 outbreak highlighted the need to prepare for future Disease X threats.
In summary, Disease X is a placeholder term used by the WHO to represent an unknown pathogen that could cause a future epidemic or pandemic. It is meant to encourage research and preparedness for the inevitable threat of emerging infectious diseases.