Public health agencies and governments across the globe are always readying their response for the next infectious disease emergency, but how do we prepare for the truly unknown? Enter Disease X.
Since 2018, this mysterious—and often misrepresented—hypothetical pathogen has been at the heart of international pandemic preparedness efforts. Planning for the emergence of an as-yet unknown infectious pathogen could mean a swifter, more effective public health response—one that readily yields the vaccines, treatments, and diagnostic tests needed to save lives.
In this Q&A, Amesh Adalja, MD, a senior scholar at the Johns Hopkins Center for Health Security, breaks down the specifics of Disease X, when and where the next potential pathogenic threat could arise, and how conceptual preparedness events could help forge new paths in pandemic prevention—and avoid repeating past mistakes.
Tell us about Disease X. How does it prepare us for future pandemics?
Secretary of Defense Donald Rumsfeld once said, there are known knowns, known unknowns, and unknown unknowns. With Disease X, we’re preparing for an unknown unknown.
Disease X is a placeholder concept that refers to a pandemic pathogen that has not yet been characterized. Its purpose is to encourage proactive thinking about pathogens that could cause a pandemic. It represents a way to push people’s thinking forward so that they’re not wedded to lists of prior pandemic pathogens, like influenza.
There are many pathogens that have the potential to cause a pandemic that might not yet be in humans. They often come from viral families with certain characteristics that lend themselves to becoming pandemic pathogens. The concept of Disease X allows people to proactively work in those viral families, to start thinking about how they are transmitted, how they impact the human body, what types of immune responses are important. All of that can start ahead of time, which increases our resiliency because people aren’t waiting for something to first be characterized as a pandemic pathogen and start working on it.
What characteristics do researchers ascribe to Disease X?
There are definitely characteristics that would be likely—not every pathogen can cause a pandemic. In general, a few things need to be present. One, it’s likely to be spread through respiration, because that’s more efficient for a pathogen. People talking, laughing, coughing, sneezing—all of that is very hard for public health to intervene on, as we saw with COVID-19. It’s likely to be a virus, not bacteria or fungus. It’s likely to be something that could spill over from an animal species into a human. Or it could be a human pathogen that develops new characteristics or changes its genetics in such a way that makes it more conducive to causing a pandemic.