The coronavirus behind covid-19 has infected most people in the world, killing around and leaving about with long-term health problems. It also caused the biggest economic downturn since the Great Depression of the 1930s. Despite all this, it could have been much more devastating.
“On the scale of pandemics, covid-19 was moderate,” says at the University of Edinburgh, UK. “There will be others, and they very easily could be an awful lot worse than the one we had. This is an eventuality we should be prepared for.”
So, what infection could cause the next pandemic? Can we stop it before it does? And are we better prepared for another pandemic if we fail to stop it?
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The term “pandemic” can mean a widespread outbreak of a mild infection. But what we are really worried about is an infectious condition – sometimes referred to as disease X – that spreads rapidly around the world, infects a huge number of people and kills a significant proportion of them, as occurred in the 1918 flu pandemic.
Fast-spreading global outbreaks are most likely to be caused by a virus that spreads via the air, and respiratory viruses that can be sneezed, coughed, spoken or out are most likely to get airborne.
When the covid-19 pandemic began, there was debate about its airborne spread, but not any more. “The debate is settled,” says at the Queensland University of Technology in Brisbane, Australia, who led calls for more to be done to prevent airborne spread.
The big worry is H5N1 bird flu. A form of it has been spreading around the world in wild birds, spilling over into domestic poultry and mammals, including people. Of the nearly 1000 since 2003, around half have been fatal.
It is likely that many mild cases have been missed, meaning that the true infection-fatality rate is lower, but it is still a major threat. “At the moment, it is what keeps me up at night,” says at the University of Oxford.
Coronaviruses remain a threat too. It is also possible that the next pandemic will be caused by an unknown virus or one that significantly differs from its known relatives. In 2021, for instance, it was revealed that a type of virus previously thought to cause gut infections had been found in hospitalised with respiratory illnesses.
To cause a pandemic, however, animal viruses such as H5N1 don’t just need to be capable of infecting humans, but also to spread from person to person. In theory, every time a virus such as H5N1 infects someone, it could mutate and gain this ability – but the odds of this happening are tiny.
Such mutations can also happen in an intermediate species that is more similar to humans in certain ways than the original viral host is. For example, the covid-19 virus may have jumped from bats to raccoon dogs and evolved in them for some time before infecting people.
This is why H5N1’s spread among dairy cows in the US and the resulting cases in some people, bringing an increased risk of mutations, is so concerning. “It’s not inevitable, but the likelihood is sufficiently different to zero to worry me,” says Katzourakis.
Besides evolution via random mutations, plenty of viruses are also able to swap genes with related viruses in a process called recombination. The H1N1 virus behind the 2009 swine flu pandemic was a .
The worst-case scenario is a recombinant virus that is as good at spreading as the human flu but as lethal as the bird flu, which may have happened with the .
Many researchers think the rather than diminishing. For one, the increasing human population continues to expand into new areas, meaning greater risk of exposure to new viruses.
Global warming is forcing many animals to migrate, raising the risk of viruses jumping between species. It is also causing more extreme weather events, which often lead to infectious outbreaks and could provide a window of opportunity for a new virus.
Then there’s the growing population of domestic animals, which can incubate new viruses. In fact, the particularly nasty form of H5N1 spreading around the world at present appears to have evolved in duck farms in China. Last but not least, people are travelling ever more, meaning outbreaks can spread further faster.
There are two schools of thought when it comes to preventing another pandemic. One is that efforts should focus on finding as-yet-unknown viruses that are already infecting people, as those that can jump to people are most likely to have pandemic potential.
The other is that we should try to spot potentially dangerous viruses before they jump to people. Thousands of viruses circulate in wild animals, but it is hard to figure out which ones might be dangerous to humans, says at Temple University in Philadelphia. “It turns out that’s a really difficult question that we don’t know how to answer,” he says.
Trying to answer it means doing experiments with live viruses, says Pond, which has an element of risk. While there is no evidence that the covid-19 virus escaped from a lab, such incidents may have happened. For instance, the flu pandemic that began in the Soviet Union in 1977 could have been caused by a strain frozen since 1950 .
While the risks are vanishingly small, the outcomes are potentially catastrophic, says Pond. “Say you run a million experiments and they go fine, but one of them does not go fine, and then you kill 10 million people,” he says. “That is unacceptable.”
Others see the risk-benefit balance differently. “There are always risks in any research, but I think what we learn about viruses from that research far outweighs those risks,” says Katzourakis.
Earlier this year, on some research, but a lab escape could occur in any country. “More regulations should be put in place and high-ranking scientific journals should stop publishing risky research,” says Virginie Courtier at Paris City University, France.
Rather than hunting for viruses in animals, Pond thinks resources are better focused on looking for viruses that are already infecting people. This could not only help identify viruses that might be capable of causing a pandemic, but could even help us nip one in the bud – as was achieved with the SARS outbreak that started in China in 2003.
But as recent human H5N1 cases in places like California and Missouri show, the next pandemic could emerge anywhere. What’s more, if a new kind of respiratory virus does start passing between people, there might be a short window of opportunity for stopping it before it spreads more widely – perhaps just weeks, say Woolhouse.
“That means you have to have surveillance systems in place that pick these things up unbelievably fast,” he says. “And, at the moment, we don’t have a system that could do that.”
There are some promising technologies, such as monitoring sewage for new viruses, but doing this more systematically on a global scale would be expensive.
The focus is instead on quickly developing tests, treatments and vaccines once another pandemic begins. This is the “100 day mission” of the International Pandemic Preparedness Secretariat that has been set up by the G7 nations.
“Maybe that’s the right decision,” says Woolhouse. But he thinks the idea of snuffing out pandemics before they grow should be kept on the table. If we fail to avert another pandemic, our health systems may at least deal with it better. A survey of researchers by the Abbott Pandemic Defense Coalition found that 60 per cent think we are .
Woolhouse thinks so too, but says much more needs to be done. “We certainly haven’t reached where we think we ought to be in terms of the public health response,” he says. For instance, the response to mpox has been lacking, he says.
Technologies also need improving. For example, while the mRNA covid-19 vaccines have saved millions of lives, they have failed to halt the pandemic altogether. Ideally, we need vaccines capable of stopping the transmission of respiratory viruses, as well as reducing their severity.
There is another major issue that is even harder to tackle. According to the Abbott survey – which was done long before the recent US election – researchers’ single biggest worry about the next pandemic isn’t surveillance or developing a vaccine, but public trust and misinformation. The fear is that if there is another pandemic, far more people will ignore health advice, such as to wear a mask, or will refuse vaccines.
“The way people behave in terms of taking precautions, managing their own risk, that’s crucial,” says Woolhouse.
“I am really worried about the misinformation,” says Katzourakis. “I’m not hugely optimistic about the incoming US administration’s likelihood of managing a pandemic effectively.
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