It’s the stuff of nightmares. As climate change accelerates, scientists are beginning to uncover ‘zombie viruses’ in the melting permafrost.

Although the name sounds terrifying, don’t panic just yet — the zombie apocalypse is not upon us. Viruses found in the Siberian permafrost – the permanently frozen layer of soil that isn’t supposed to thaw, even in summer – have been named “zombie viruses” because they were dormant (sort of “undead”), but scientists are now bringing them back to life.

In fact, scientists have already dusted off thirteen viruses from their icy sleep so far.

Pandoravirus Yedoma: The Granddaddy of ‘Zombie Viruses’

Ever wondered what a 48,500-year-old virus looks like? Meet Pandoravirus yedoma – eerily named, of course, after Pandora’s Box –  the oldest virus ever to wake up from its icy slumber.

Scientists found Pandoravirus yedoma under an icy lake in the Russian Far East in 2022. Pandoraviruses are the biggest viruses known, with a supersized DNA that contains up to 2,500 genes (compared with just ten genes in many viruses). Pandoravirus yedoma quickly woke up from its sleep when introduced to a one-cell organism, infecting it within minutes.

Pithovirus Sibericum: The Sleeping Giant Awakens

In 2000, researchers came across Pithovirus sibericum, snuggled deep within the permafrost of Kolyma, Russia. At around 1.5 micrometers (1000 times smaller than a millimeter) long, it might sound small. In the world of viruses, Pithovirus Sibericum is quite a giant.

After scientists found the 30,000-year-old virus, they introduced it to some amoebas — and the virus came back to life. But don’t worry just yet — for now Pithovirus Sibericum can only infect amoebas. Humans (and our furry friends) are off the menu.

Pithovirus sibericum sketch

Pithovirus sibericum sketch. Credit: Pavel Hrdlička Via Wikimedia Commons (CC BY-SA 3.0).

Scientists felt elated, as they had seen a virus that remained infectious for so long for the first time. But many more virus discoveries were soon to follow.

Mollivirus Sibericum: It’s a Small World After All

It’s not the size that makes the virus, though. Discovered at the same time as P. sibericum, Mollivirus sibericum is a much smaller virus — but once it attacks an amoeba, it can produce 200 to 300 viral particles.

Again, don’t lose sleep over it. M. sibericum poses no threat to humans or other animals. But its discovery does make researchers wonder — what else is lurking in the Siberian wilderness?

It’s Getting Hot in Here

Well, that’s a tricky question. Siberia is warming at nearly four times the global average rate and also experiencing intense wildfires. In July 2023 alone, “110 forest fires were raging across about 61,000 hectares, roughly three-quarters the size of New York City.

The soaring temperatures are melting the region’s permafrost. As the ice melts, a Pandora’s box of ancient viruses is coming up to the surface.

While the viruses recovered so far can only infect amoebas, there’s no way to know what else is lurking in the ice — including viruses that could potentially jump to humans and animals.

Smallpox — which killed over 300 million people in the 20th century alone and was eradicated in 1980 — can survive freezing temperatures, so if scientists ever run into infected centuries-old human remains, it’s possible the virus could come back to life.

The scientists who studied Mollivirus sibericum believe the danger is real. In a 2015 study, they point out that while the viruses recovered so far can’t hurt us, “we cannot rule out that distant viruses of ancient Siberian human (or animal) populations could reemerge as arctic permafrost layers melt and/or are disrupted by industrial activities.

So, while the term ‘zombie viruses’ may sound like something from a horror movie, the truth is that as our planet continues to warm, we must prepare for what we might unearth.

By Diana Bocco, contributor for


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