Half of all people outside Africa carry a gene variant inherited from Neanderthals that reduces the risk of needing intensive care for COVID-19 by 20 per cent, says a new study.

In addition to risk factors such as old age and diabetes, the scientists, including those from Karolinska Institute in Sweden, said gene variants in people also make them more or less sensitive to developing severe COVID-19.

While an earlier study by the researchers showed that this risk variant is inherited from Neanderthals, the current research, published in the journal PNAS, says these human ancestors also contributed a protective genetic variant to present-day people.

According to scientists, this variant, which reduces the risk of needing intensive care upon infection with the virus by 20 percent, is inherited from Neanderthals.

The genes, called OAS, regulate the activity of a protein that breaks down viral genomes, and the study noted that the Neanderthal variant of this protein does this more efficiently.

“This shows that our heritage from Neanderthals is a double-edged sword when it comes to our response to SARS-CoV-2. They have given us variants that we can both curse and thank them for,” said Hugo Zeberg, a co-author of the study from Karolinska Institute.

The study also shows that the protective variant from Neanderthals has increased in frequency since the last Ice Age so that it is now carried by about half of all people outside Africa.

“It is striking that this Neanderthal gene variant has become so common in many parts of the world. This suggests that it has been favourable in the past,” said Svante Paabo, director at the Max Planck Institute for Evolutionary Anthropology.