A scanning electron microscope image showing SARS-CoV-2 (round blue objects) emerging from the surface of cells cultured in the lab.  Image credit: NIAID
“Disease X” is appearing all over social media and news feeds once again. So, what actually is Disease X? Why is everyone talking about it? And is it anything to be concerned about?

What is Disease X?
The term “Disease X” is used by some scientists and the World Health Organization (WHO) to refer to unknown pathogens that have the potential to cause a serious international epidemic on the scale of COVID-19 or worse. 

The term is not new. The WHO first used it around 2018, but it was reignited in the public imagination when COVID-19 arrived on the scene, starkly highlighting the need for pandemic preparedness. Indeed, some scientists even argued that COVID-19 could be considered as the “first Disease X” because it was a novel disease, unknown to science when it first started infecting humans. 

What might the next Disease X be?
That’s the thing: no one knows. 

The WHO has a priority list of known pathogens that have the potential to spark a major global disease outbreak, including Crimean-Congo hemorrhagic fever, Ebola, Marburg virus disease, Lassa fever, Nipah and henipaviral diseases, Rift Valley fever, Zika, and Middle East respiratory syndrome coronavirus (MERS-CoV), Severe Acute Respiratory Syndrome (SARS), and COVID-19.

The priority list also includes Disease X, a placeholder name for a novel infectious agent that is not yet on the radar of any scientists. 

It’s treated as a “known unknown”, to quote the infamous speech by US Secretary of Defense Donald Rumsfeld in 2002. The exact nature of the threat is not clear, but it’s evident a threat is out there. 

Perhaps a relative of the pathogen is already out there; existing undiscovered in a natural reservoir, “waiting” for the right mutation (and chance) that will allow it to spill over into humans. Quite simply, we don’t know yet. 

Why are people talking about Disease X now?
Disease X was recently the subject of an expert panel discussion at the 2024 World Economic Forum meeting in Davos, which featured Dr Tedros Adhanom Ghebreyesus, the WHO director-general. 

This has brewed some conspiracy theories along the lines of “global elites preparing to release Disease X”. However, that’s a total distortion of what was said. In reality, the talk was simply about preparing for the next pandemic, which is almost inevitable (just as it always has been throughout human history).

“Disease X is a placeholder for an unknown disease… Although COVID came immediately, we were preparing for COVID-like diseases. You may even COVID as the ‘first Disease X’ – and it may happen again,” said Dr Tedros.

“Of course, there are some people that say this may create panic. No. It’s better to anticipate something that may happen – because it has happened in our history many times – and prepare for it,” he added.

Should you be worried about Disease X?

Well, in short, yes. However, there’s no need to panic – you certainly don’t need to raid the supermarkets for toilet paper. 

Once again, it is almost inevitable there will be another global pandemic in the future. Disease outbreaks have riddled humanity throughout history and continually molded the shape of societies around the world. 

In the 21st century, the risk of a pandemic is even higher since we live in a hyper-connected, globalized, and urbanized world that creates the ideal setting for an infectious pathogen to run riot across millions of people. Furthermore, humanity’s increasing infringement on the natural world is increasing the odds that it will run into potential pathogens and a spillover event will occur. 

The good news is that the world is already taking steps to brace itself for the next pandemic, through an array of preparedness, prevention, and response measures. Hopefully, we also learned some good lessons about how to – and how not to – deal with it.