The couple trying to keep killer ‘zombie viruses’ at bay – and protect us from another pandemic

Jean-Michel Claverie was already at retirement age when he travelled to Siberia to hunt for ancient viruses in the Arctic. After a long career as a research scientist – and 25 years since he had set up a laboratory outside Marseille with his wife Chantal Abergel – he could have put his feet up. He and Abergel, who is 62, commute to their lab from a comfortable house near the pretty harbour town of Cassis. But Claverie, who was about to turn 70, had no intention of hanging up his lab coat.

It took days, several flights and a ride in a rickety boat made from old war plane parts to reach the banks of the Kolyma river west of Chersky, a remote town not far from the East Siberian Sea. Once a transit hub for Soviet Gulags, Chersky and its river had become a magnet for scientists trying to unearth secrets from the frozen deep. 

At a tight bend in the river he set up a makeshift research station inside a tent and from there, he and a small team began removing soil from the steep-sided riverbank to expose earth that has been frozen for 30,000 years.

A layer of this hardened soil and sand, known as permafrost, lies beneath the earth’s surface across vast areas of the northern hemisphere, largely in Arctic regions of Russia, Scandinavia and North America. In places such as Chersky, the permafrost stays below freezing even while the summers are hot and the surface landscape verdant. In some Arctic regions, life in this layer has been suspended for around 700,000 years.

But climate change and rising temperatures mean that permafrost is now thawing. As a result, powers including Russia, China and the US are stepping up efforts to drill and dig through it in pursuit of precious metals and fossil fuels. 

Suspended within this thinning layer, however, are the preserved remnants of prehistoric life. Some of it – including viruses – may yet return from the dead with unknown consequences.

I meet Claverie, who is now 73 and wears blue jeans and running shoes, in the genomic and structural information lab at Aix-Marseille University, where he is now a professor emeritus. He and Abergel, an experimental biologist who runs the lab, lead an international team of a dozen researchers in a stout concrete building on a hilltop campus between Marseille and Cassis.

Inside a small lab with a yellow biohazard danger sign on the door, alongside the logo for the Back to the Future film, Claverie pulls a small plastic bag out of a freezer. It contains what looks like the damp remains of a sandcastle. It is in fact thawed Siberian permafrost. During his two-week field trip, Claverie’s team used a drill with a cup-shaped coring bit to prize more than 20 such samples from the banks of the Kolyma. He brought them back to the French Riviera in his suitcase.

The team study these, as well as permafrost samples already stored in scientific institutes, in a race to understand the microbes suspended within them. While virology research tends to focus on threats lurking in more tropical climates, Claverie and Abergel are searching for potential dangers now emerging from the frozen north, including what have become known as ‘zombie viruses’.

‘The real danger would be to be confronted with viruses we’ve never seen before,’ Claverie tells me in the lab, where a low winter sun streams through a high window. He points out that we still don’t know for certain what role viruses might have played in the demise of major species such as Neanderthals or woolly rhinos. 

And consider, he says, the huge efforts required to suppress pathogens already familiar to science, such as the coronaviruses. ‘So think about a totally new virus that might have caused [an] extinction. What happens if it comes back?’

Claverie and Abergel fell in love at a science conference in a French ski resort in 1987. They were both interested in the then emerging field of bioinformatics – the use of computers to make sense of biological data. In 1995, after working in the US for five years, the couple settled in Marseille, where Abergel had grown up, to establish their lab. They now have two grown-up sons – a chef and an engineer.

The couple occupy neighbouring offices above the labs. ‘We had to work together at home in the pandemic and Jean-Michel was upset because I was making too much noise,’ Abergel tells me at her desk, which is next to a vast potted Flamboyant tree she planted as a seed. ‘It is very capricious and has never flowered,’ she adds with a smile.

Claverie had enjoyed an early career as a nomadic researcher in multiple fields, including theoretical physics. The lab’s early work involved the sequencing of bacterial genomes – the genetic information that defines organisms. The switch to virus research was accidental. A sample that had originally come from a hospital in Bradford as part of a search for the origins of a pneumonia outbreak contained what scientists had assumed was a new type of bacteria. On closer inspection in Marseille, the bacteria turned out to be a virus that broke all the rules.

There are more viruses than stars in the universe and most remain undiscovered. They lurk anywhere there is life – in the sea, soil and air – but only replicate when they meet a host. They were always thought to be tiny and genetically simple, containing only what they needed to invade cells, replicate and move on. The new microbe from Bradford was orders of magnitude larger and more complex than any known virus. ‘I can still remember when we got the image from the microscope,’ Claverie recalls. ‘I said, “Jesus, what is this?!”’

They named it Mimivirus. The discovery stunned the field of virology, which was concerned largely with diseases caused by viruses in humans, livestock and agriculture. Viruses existing in the wild without a known host had flown under the radar. Mimivirus opened a new field of research. ‘This was the start of environmental virology,’ says Claverie, who quickly refocused his lab’s work.

For several years, the team discovered more giant viruses, which they helped detect by introducing amoebas to samples; if the single-cell organisms died, it signalled the presence of a virus and the need for further research. This work, which added to wider understanding of viruses and how they interact with hosts, found a new avenue in 2013 when Claverie read a Russian paper about the regeneration of a plant from fruit tissue that had been frozen in the Siberian permafrost for 30,000 years. ‘I thought, if they can revive a plant, can we revive a virus?’

The ground floor of the building in Marseille is divided into a series of modest labs, many cluttered with microscopes, chemicals, glass flasks and beakers. While Claverie is the de facto chief virus hunter, Abergel has led the development of the techniques used to isolate and study them. ‘We complement each other well, even if we sometimes fight,’ she says. ‘We’re both stubborn and, like all scientists, we always think we’re right.’

Machines and air-conditioning units hum in the background, maintaining climates for each stage of the process. One of the machines, called a ‘mosquito robot’, incorporates 96 needles capable of inserting virus proteins into wells containing different culture conditions. In another room, the amoebas that are used as bait to catch viruses are grown and stored. When a virus is detected in a sample, technicians purify and amplify it before its DNA can be sequenced.

Claverie can’t remember who first used the word ‘zombie’ in relation to his virus work. Certainly it did not appear in his landmark paper in 2014, which detailed the first revival of a virus preserved in permafrost. He named the microbe, which he found in an existing, 30,000-year-old sample taken from ground not far from Chersky, ‘Pithovirus sibericum’. Not long after the discovery, a specialist toy company made a stuffed Pithovirus, added a cute smile, and called it Zombie Virus. ‘The whole thing started going crazy,’ Claverie says.

The sci-fi name challenged Claverie’s academic instincts but it has also amplified his and Abergel’s research over a decade in which the climate crisis has become more urgent. The couple have continued to revive more than a dozen distinct viruses from permafrost, including in the last meals found in the frozen stomachs of woolly mammoths. In one case they reanimated a virus that had hibernated for 50,000 years.

None of these viruses would pose a risk to humans even beyond the controlled environment of the Marseille lab; they are specific to their amoeba hosts. But the scientists are anxious to raise awareness of potential threats that may still emerge. ‘If there are viruses that have been preserved for 50,000 years, there will probably be others from long before that,’ Claverie says. ‘The human species is only 200,000 years old. We don’t know what kind of viruses existed before that and we’re certain our immune systems were never exposed to them.’

There have been early warning signs of the health effects of climate change in the Arctic. In 2016, a young boy and thousands of livestock died in the Yamal-Nenets region of Russia when a reindeer that had been dead for decades thawed in a record heatwave, releasing the anthrax bacteria.

Scientists fear that centuries-old shallow graves that herders used for livestock (firewood being too scarce to burn carcasses) may become anthrax infection sites, although the disease is not contagious between people. Meanwhile, the DNA of the smallpox and influenza viruses has been detected in human corpses that had been frozen for over a century. Those samples were not revived and even the deadliest virus poses no threat if it remains locked in permafrost. But Claverie fears that this may be about to change.

Over the past four decades, the Arctic has warmed up four times faster than the global average – and up to seven times faster in parts of Norway and Russia. A doom loop known as Arctic amplification involves the absorption of more sunlight as a result of the loss of reflective ice, leading to further warming and melting.

Melting ice is bad news for polar bears and other Arctic fauna but there is perhaps less awareness of the effects of thawing permafrost. Earth that has been frozen solid is turning to mud, causing giant sinkholes to open up. Phone lines, roads, airport runways and whole towns are at risk. 

Meanwhile, the thawing of organic matter within permafrost is releasing vast quantities of methane, creating a second vicious cycle as the potent greenhouse gas exacerbates global warming. These effects strike fear into the hearts of scientists, but present opportunities to businesses and nations still struggling to break bad habits. Melting sea ice is opening up shipping routes to support growing industrial exploitation of thawing ground that is becoming more viable as a source of minerals and fuel.

Russian nuclear-powered icebreakers are supplying plants that make up the growing Yamal liquified natural gas project. In Norway, Canada and the US, prospectors are eyeing up Arctic ground for the precious and rare metals and minerals needed to power technology such as batteries for electric vehicles. As workforces the size of large towns gather at these sites, Claverie worries about the potential threat of exposure to viruses that may be churned up in the course of drilling and digging.

‘There are a lot of sharks in Australia, but if you don’t go surfing, that’s fine,’ he says, reaching for a metaphor from an even warmer climate to illustrate the point that there is no danger without exposure to an underlying hazard. ‘But now, with the development of industrial activities in the Arctic, we are going to have contact with these things.’

Then there are the effects of Covid. The pandemic has been positive for investment in viral research, but Claverie is also concerned that this is bringing us closer to danger. Parts of the scientific community are going out in search of exotic viruses that they know are deadly to humans. Yet one bite from a bat in the field, or a slip of a needle, is all it can take for a disastrous outbreak to occur.

Claverie shows me two photos from an Arctic research centre in which a baby mammoth carcass is laid out on a slab. In the official image, scientists wear masks and full-body protective suits. In another snap taken privately, a small crowd in everyday clothing gathers around the animal as if it were an item on Antiques Roadshow. ‘There are scientists in Russia who are already trying to revive viruses that infected mammoths and woolly rhinos,’ the professor adds. ‘This is totally stupid and dangerous. You do not revive viruses that infect animals.’

Claverie is part of an increasingly vocal campaign within the science community to prioritise surveillance over prospecting, finding sick patients early rather than investing millions in the risky search for pathogens in the wild. The Marseille lab is now part of UArctic, a consortium of educational institutes that is working to establish a monitoring network and quarantine protocols in the event of an infection from a permafrost virus. ‘The idea is that you capture the virus before it becomes a pandemic.’

Yet scientific cooperation with Russia, which has the largest share of permafrost (two-thirds of the country sits above it), has been on ice since the invasion of Ukraine in 2022, blocking access to researchers and samples. Claverie is worried about this collaborative breakdown, as well as Putin’s disregard for climate targets and rush to exploit Arctic resources. ‘My trip was funded partly by the Russian Academy of Sciences,’ he says. ‘Those things don’t exist any more, they are frozen.’

Up in Claverie’s own office, fragments of mammoth bones sit on a bookshelf. The professor smuggled them out of Russia along with his permafrost samples in 2019. He is glad he was able to make it to Siberia before the pandemic and the Ukraine invasion. Either way, he sees no reason to return now he has proved his point: that the world should be alert to the viruses that may be released from thawing permafrost.

He has grave concerns about the future but does not come across as a doomsayer; he is driven by a natural curiosity and passion for science. Work at the lab goes on to find viruses in existing samples, including thousands stored at a polar research institute near Hamburg. Meanwhile, he has expanded his interest south to Antarctica.

He tells me he has already made promising discoveries in samples of sediment he asked scientists on an Italian research vessel to retrieve from beneath the Ross Sea in 2022. Only a last-minute change of the expedition’s budget prevented him from travelling to the frozen south himself. As he sails through his notional retirement in Marseille, he says Abergel’s relative youth, apart from anything else, keeps him working. ‘Perhaps when she retires I will stop, but until then I’m not going to go on a cruise by myself,’ he says, before returning to his screen.