Next up: the sewers, one of the places Bray suggests we should be looking for pathogens. Here again, there’s a precedent. In 2013, sewer sampling caught a silent epidemic of a poliovirus in Israel, triggering a vaccination campaign that helped to avert a more serious outbreak of polio. Now, across Europe and the US, wastewater testing for COVID-19 is helping scientists to get an unbiased picture of how the virus spreads.

Italian researchers, for example, retrospectively analysed samples of raw sewage collected before the first wave officially began, detecting traces of the virus in samples from three Italian cities in December and January, weeks before the first non-imported case was reported in late February. And according to Prof Dragan Savic, CEO at KWR Water Research Institute in Nieuwegein, the Netherlands, we’re already looking at levels of new variants.

Sewage, Savic explains, provides a window on literally everyone’s business. So you don’t have to wait for mass testing to get up and running, or worry about whether people are testing when they should be. “There are people who don’t have symptoms, there are people who are recovering – who will not go for testing – and there are limited tests,” he says. “But we all go to the toilet, so when you think about it, that’s unbiased sampling.”

So our wastewater can give us a heads-up when an emerging disease first infects a new area. With AI, the same information could also be combined with other data sources, like weather patterns or gatherings of people, to help reveal how an infectious agent is spreading and plan allocation of resources.

Biosensing networks

Another key component of Bray’s system is a biosensing network that he envisions being embedded into plants and animals. In his 2021 scheme, he describes transmissions from these biosensors feeding into a supercomputing network. Such biosensors aren’t fantastical; they are promising and, in some cases, already commercially developed devices (think glucose sensors for diabetes) based on biological components. They’re set to make a big impact as “low-cost sensing systems that can be deployed in the field”, according to synthetic biologist Prof Paul Freemont, who is developing biosensors at Imperial College London.

Freemont’s biosensors are fluorescent beads that lose their fluorescence when they contact proteases, which are enzymes used by a wide variety of organisms. Many viruses, from HIV to herpes, use proteases to replicate. Freemont has tailored them to detect different targets, including proteases from a plant virus, as well as from Schistosoma mansoni, a parasitic worm. The technology uses components that the researchers suggest could be modified to detect different pathogens, perhaps in portable devices in regions where the risk of animal diseases crossing over into humans is high.

However, embedding biosensors into plants and animals may be taking the idea too far for Freemont. He isn’t convinced that biosensors would help us get ahead of a new disease. “My question is: how can we embed sensors to detect things that we know nothing about?” he says. “It could be useful for existing targets, for sure, and for emerging targets that we know of, but the problem is something completely new. Would you have enough time to redesign that system and get it back into the wild?”

It’s a good question. Our immune systems don’t just respond to bacteria and viruses that they’ve met before. They detect and protect us against any foreign invader, using receptors that distinguish between ‘self’ (us) and ‘non-self’ (invaders). It’s hard to envisage how we might replicate this system on a planetary scale. But we need to be able to work out what, from the multitude of unknowns, might pose the biggest threats. This, Bray says, will be “the most novel part” of the system.

Genome observatory

Dr Kevin Esvelt, a biochemist at the Massachusetts Institute of Technology, has his own ideas about how we should detect new and dangerous pathogens. His theories are aimed primarily at dealing with what he calls “the deliberate variety” of pandemic – to his mind a more difficult problem than a naturally occurring one. Why? Because, he says, bioterrorists have to be expected to design weapons to evade any defences that we might set up. We therefore need a more open approach in order to detect this stuff; one that would catch not just new variants of old diseases, but something the like of which we’ve never seen.

In a pre-print paper published on arXiv in August 2021, Esvelt proposes a global Nucleic Acid Observatory that would sequence the genomes of everything we encounter in the sewer space and beyond. But how would this approach help us to pinpoint those organisms we need to be particularly wary of? As the paper outlines, the real hallmark of any organism with pandemic potential is unbridled growth, which would be seen as an explosion in levels of its genome sequences.

“Any serious threat must by definition grow exponentially,” Esvelt explains. “This should allow us to detect anything potentially problematic, be it an invasive pest, a crop blight, a novel pandemic virus unrelated to anything we’ve seen before, or even something totally new that [an] adversary has devised.”

Perhaps something like this observatory could form a key part of the immune system for the planet? Freemont, for his part, says it’s a “compelling” proposition for solving the problem of detecting entirely new pathogens. Yet to do all of this, we’d need armies of sample collectors to mail samples back to the lab every few days. Compared to the seamless detection system that Bray imagines, this does seem rather laborious.

But Esvelt argues it would be worth it. “Doing this for next-day sequencing is a tiny cost relative to that of the sequencing itself, and losing a day in exchange for reliability is an excellent trade-off,” he says.

Sequencing won’t tell us everything though. Any candidates with pandemic potential would have to be probed in exquisite, molecular-level detail, not just to work out whether they’re real threats, but also how we might tackle them. “That’s going to involve some research,” Bray admits.

At Washington State University, a project called Deep VZN is already aiming to do something similar. Deep VZN will characterise thousands of viruses from wild animals across 12 countries, focusing on the families of viruses that spawned COVID-19, Ebola and measles.

Project leader Dr Felix Lankester says his team plans to probe the molecular structure of those whose genomes are “unknown”, looking for a lock-and-key type fit between molecules on the surface of viruses and receptors on human cells. They will also use an algorithm to assess the likelihood of the viruses spilling over into humans and look at whether these viruses could evade or inhibit our immune defences. “This information will be made available for the design and development of countermeasures, such as new vaccines and diagnostics,” says Lankester.

In the future, Bray anticipates a lot more of the work being done by machines. With AI programs like DeepMind’s AlphaFold already making huge strides in predicting the 3D structures of proteins, such thinking might not be such a stretch. So, if you leave aside the difficulty of predicting how symptoms might play out in real humans (before any have actually been infected), all of this might sound quite feasible, eventually.

It’s when we get to Bray’s ideas about how we should respond to such threats that things get a bit wild. He would have us rolling out machine-designed vaccines at the touch of a button and even suggests distributing antibodies in drinking water, a step that would seem less drastic if we were talking about something more dangerous than COVID. Which he is.

“We’re not talking about a slow-spreading pandemic like we have now. It’s one where you would have an hour or less to survive,” he says, suggesting that the first place to trial this would be in countering the use of bioweapons on military battlefields.

The question is: will policymakers be persuaded to think ahead on pandemics? Even post-COVID, warnings of epidemiologists are still ignored, Cleaveland points out. Hendra virus, a bat disease that can be fatal to horses and humans if it spills over, is a case in point.

In 2020, Australian and US researchers warned of a high risk of spillover during the coming winter, but to no avail. “For me that was a really fascinating insight,” she says. “We have a vaccine. This is a fatal disease. We had a good indication that there was a risk coming and still, people didn’t respond.” Luckily, things turned out okay, but only because the bats were kept at bay by an unexpected crop of fruit.

So if policymakers aren’t willing to act, who is going to invest in the immune system for the planet? “Can we find a coalition of the willing?” asks Bray. It’s always going to be a hard sell because if it works, nothing will happen – preventing a pandemic just looks like a colossal waste of cash. Unless, maybe, you’re still reeling from the financial fallout from the last one.

• This article first appeared in issue 375 of BBC Science Focus Magazine – find out how to subscribe here

Read more about COVID-19:

• You’re not alone: The pandemic has ruined all of our sleep
• What can the world do to avoid future pandemics like COVID-19?
• Has the pandemic unleashed a plague of rats on our cities?

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