Might as well just call it 'Captain Tripps'.

Two mainstream media takes -

Unknown 'Disease X' flagged by World Health Organization, could cause 'serious international epidemic'

Scientists warn that an unknown "Disease X" poses a major health risk and could cause a "serious international epidemic" in the future.
Disease X was listed by the World Health Organization as one of eight priority diseases. Others on the list include Ebola, Zika and Lassa fever.

What is Disease X?
Disease X is not a newly identified pathogen but what military planners call a “known unknown”. It’s a disease sparked by a biological mutation, or perhaps an accident or terror attack, that catches the world by surprise and spreads fast.
By including it on the list, the WHO is acknowledging that infectious diseases and the epidemics they spawn are inherently unpredictable. Like the Spanish flu which killed 50m to 100m people between 1918 and 1920, Disease X is the catastrophe nobody saw coming until it was too late.
Where might it come from?
One source of Disease X could be the deliberate utilisation of infectious disease as a weapon.
While bio-weapons have been used since the middle ages (the Tartars catapulted the cadavers of plague victims into the besieged seaport of Caffa in 1346, for example), new scientific developments including gene editing and an exponential increase in computing power make it easier than ever to develop lethal biological agents.
The US and USSR explored bio-weapon development during the Cold War and both continue to hold live cultures of deadly pathogens, including the smallpox virus, in secretive and (hopefully) secure labs. More recently, the Iraqi military toyed with botulinum toxins under Saddam Hussein, Al Qaeda operatives experimented with anthrax and, in 2014, a laptop captured from Islamic State (IS) was found to contain instructions on how to weaponise the plague virus.

From WHO -

World Health Organization 2018 annual review of the Blueprint list of priority diseases