Disease X is a placeholder name that was adopted by the World Health Organization (WHO) in February 2018 on their shortlist of blueprint priority diseases to represent a hypothetical, unknown pathogen that could cause a future epidemic. The WHO adopted the placeholder name to ensure that their planning was sufficiently flexible to adapt to an unknown pathogen (e.g., broader vaccines and manufacturing facilities). Director of the US National Institute of Allergy and Infectious Diseases Anthony Fauci stated that the concept of Disease X would encourage WHO projects to focus their research efforts on entire classes of viruses (e.g., flaviviruses), instead of just individual strains (e.g., zika virus), thus improving WHO capability to respond to unforeseen strains. In 2020, experts, including some of the WHO's own expert advisors, speculated that COVID-19, caused by the SARS-CoV-2 virus strain, met the requirements to be the first Disease X.
Rationale
In May 2015, in pandemic preparations prior to the COVID-19 pandemic, the WHO was asked by member organizations to create an "R&D Blueprint for Action to Prevent Epidemics" to generate ideas that would reduce the time lag between the identification of viral outbreaks and the approval of vaccines/treatments, to stop the outbreaks from turning into a "public health emergency". The focus was to be on the most serious emerging infectious diseases (EIDs) for which few preventive options were available. A group of global experts, the "R&D Blueprint Scientific Advisory Group", was assembled by the WHO to draft a shortlist of less than ten "blueprint priority diseases".
Since 2015, the shortlist of less than 10 EIDs has been updated annually and has consistently included widely known names such as Ebola, Zika and SARS (e.g., cause of large-scale infections), and more geographically specific names such as Lassa fever, Marburg virus, Rift Valley fever, and Nipah virus.
In February 2018, after the "2018 R&D Blueprint" meeting in Geneva, the WHO added Disease X to the shortlist as a placeholder for a "knowable unknown" pathogen. The Disease X placeholder acknowledged the potential for a future epidemic that could be caused by an unknown pathogen, and by its inclusion, challenged the WHO to ensure their planning and capabilities were flexible enough to adapt to such an event.
At the 2018 announcement of the updated shortlist of blueprint priority diseases, the WHO said: "Disease X represents the knowledge that a serious international epidemic could be caused by a pathogen currently unknown to cause human disease". John-Arne Røttingen, of the R&D Blueprint Special Advisory Group, said: "History tells us that it is likely the next big outbreak will be something we have not seen before", and "It may seem strange to be adding an 'X' but the point is to make sure we prepare and plan flexibly in terms of vaccines and diagnostic tests. We want to see 'plug and play' platforms developed which will work for any or a wide number of diseases; systems that will allow us to create countermeasures at speed". US expert Anthony Fauci said: "WHO recognizes it must 'nimbly move' and this involves creating platform technologies", and that to develop such platforms, WHO would have to research entire classes of viruses, highlighting flaviviruses. He added: "If you develop an understanding of the commonalities of those, you can respond more rapidly".
Adoption
Jonathan D. Quick, the author of End of Epidemics, described the WHO's act of naming Disease X as "wise in terms of communicating risk", saying "panic and complacency are the hallmarks of the world's response to infectious diseases, with complacency currently in the ascendance". Women's Health wrote that the establishment of the term "might seem like an uncool move designed to incite panic" but that the whole purpose of including it on the list was to "get it on people's radars".
Richard Hatchett of the Coalition for Epidemic Preparedness Innovations (CEPI), wrote "It might sound like science fiction, but Disease X is something we must prepare for", noting that despite the success in controlling the 2014 Western African Ebola virus epidemic, strains of the disease had returned in 2018. In February 2019, CEPI announced funding of US$34 million to the German-based CureVac biopharmaceutical company to develop an "RNA Printer prototype", that CEPI said could "prepare for rapid response to unknown pathogens (i.e., Disease X)".