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CNN  — 

People who survive a bout of Covid-19 with mild symptoms or even no symptoms may be able to thank their Neanderthal ancestors, a new study suggests.

Researchers found a genetic mutation that reduces the risk of severe Covid-19 infection by about 22%. It was found in all the samples they took of Neanderthal DNA, and in about 30% of samples from people of European and Asian origin.

The genetic region involved affects the body’s immune response to RNA viruses such as the coronavirus, as well as West Nile virus and hepatitis C virus, the researchers reported Tuesday in the Proceedings of the National Academy of Sciences.

“This region encodes proteins that activate enzymes that are important during infections with RNA viruses,” they wrote.

It may be one of those mutations that has been passed down over the millennia because it helped people survive, Svante Paabo and Hugo Zeberg of the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany reported.

“We show that a haplotype on chromosome 12, which is associated with about a 22% reduction in relative risk of becoming severely ill with COVID-19 when infected by SARS-CoV-2, is inherited from Neandertals,” they wrote. “The relative risk of needing intensive care is reduced by about 22% per copy of the Neandertal haplotype,” they added.

“This haplotype is present at substantial frequencies in all regions of the world outside Africa,” they added. “It is present in populations in Eurasia and the Americas at carrier frequencies that often reach and exceed 50%.”

The finding could help explain why Black patients are so much more likely to suffer severe coronavirus disease. Neanderthals, who went extinct about 40,000 years ago, lived alongside and sometimes interbred with modern humans in Europe and Asia but not in Africa, and people of purely African descent do not carry Neanderthal DNA. Studies estimate that about 2% of DNA in people of European and Asian descent can be traced back to Neanderthals.

The team used samples taken from more than 2,200 living people with severe cases of coronavirus or matched controls. They found a genetic region that affected susceptibility to severe disease. Then they checked the DNA taken from the skeletons of four ancient humans – a 70,000-year-old Neanderthal from Siberia, a 50,000-year-old Neanderthal from Croatia, a 120,000-year-old Neanderthal from Denisova Cave in Siberia and an 80,000-year old sample from the same site from a Denisovan – another sub-species of ancient human. All four samples carried the same versions of that genetic sequence.

Last year, Paabo and Zeberg identified a genetic mutation inherited from Neanderthals that raised the risk of serious disease. As with most traits, susceptibility to disease and to serious outcomes is affected by a variety of genetic differences.