We don't know its name. We don't know where it will begin, nor when it will end. But we know it's almost certainly coming for us.
Now, scientists have unveiled a blueprint of what the next deadly global pandemic will probably look like, with over 120 experts sharing insights on the predicted traits of a virulent future pathogen that will know no borders.
"We need to get serious about respiratory viruses," infectious diseases researcher Amesh Adalja from Johns Hopkins University told Live Science.
"[There's] a lot of focus on diseases that aren't going to be able to change civilisation in a way that something that's spread through the respiratory route would be."
The kinds of diseases Adalja is talking about – things like Zika virus and Ebola – are extremely serious threats to public health, but in terms of pathogens that could pose a global catastrophic biological risk (GCBR), they're not as severe as biological agents that can freely disperse through the air we breathe.
That's the conclusion of a new report led by Adalja and released by the Johns Hopkins Centre for Health Security, which looks at the characteristics of pandemic pathogens.
According to the findings, perhaps the greatest threat of such a catastrophic pandemic isn't the bug itself – whose ultimate emergence is out of our hands (probably). Instead, it's us.
Why? Because a huge amount of research into things like viral forecasting goes into cataloguing, investigating, and sequencing the infectious threats we already know about.
While that's great for scientific understanding, Adalja says it's debatable whether this effort actually bolsters disaster preparedness for unfamiliar biological threats we have yet to encounter, and which don't fit the set templates we're busy drawing up.
"Health security preparedness needs to be adaptable to new threats and not exclusively wedded to historical notions," Adalja explains in a statement.
"A more active-minded approach to this problem will, in the end, help guard against a GCBR event occurring."
To that end, Adalja and fellow researchers spent over a year reviewing scientific literature on emerging infectious disease characteristics and the pathogenic potential of microbes – and interviewed more than 120 technical experts from academia, industry, and government.
In the team's final analysis, they say the pathogen responsible for the next deadly global pandemic will probably spread via a respiratory mode of transmission, and would be contagious during the incubation period, prior to the development of symptoms (or when people only show mild symptoms).
The disease would most likely have a low but significant case fatality rate: an important factor that actually increases the pathogen's overall transmissibility.
In other words, it would kill some people, but most would survive contracting the infection – leaving them free to spread the pathogen to others while they remain contagious – whereas a highly fatal, quick-acting killer bug could be too deadly for its own good.
The researchers think the most dangerous GCBR-level pathogens are RNA viruses, which are capable of mutating.
If a new kind of RNA virus were to emerge and grab a foothold among immunologically compromised people in the community – and if existing medicines didn't effectively contain the infection – we could have a GCBR event on our hands, the researchers say.
"It just has to make a lot of people sick," Adalja told Live Science, adding that initial and seemingly mild symptoms can sometimes mask how serious sicknesses are.
"[It's] not always going to be somebody dying a horrible death … it could be a very minimal case."
Of course, the good news is we haven't been struck with one of these GCBRs in recent times.
Here's hoping this new report stirs some fresh debate in the scientific community, and prepares us to face the real risks out there – which may be nothing like what we've seen before.
"We approached this project with active minds trying to jettison reliance on list-based approaches that are incomplete and almost guarantee surprise outbreaks," Adalja explains in a blog post.
"I hope that others find the report of value and it serves to generate deeper analysis of this field."
The full report is available at the Johns Hopkins Centre for Health Security website.