Some people become very ill after being infected with SARS-CoV-2, while others have only mild symptoms or no symptoms at all. In addition to advanced age and chronic disease risk factors such as diabetes, our genetics also contribute to this phenomenon.

Now, a study led by Germany's Max Planck Institute for Evolutionary Anthropology (MPI-EVA) shows that the same genetic variants that increase the risk of severe illness from COVID-19 can protect against another serious disease that causes a person to become infected with HIV. The risk of the virus is reduced by 27%. The research was published in PANS.

The genetic variants we are born with can increase or decrease our risk of severe COVID-19. A major genetic risk variant for severe COVID-19, one we inherited from Neanderthals, is surprisingly common. This raises the question of whether there are actually benefits to carrying this variant.

In autumn 2020, Hugo Zeberg at Karolinska Institutet and Svante Pääbo at MPI-EVA have discovered that we inherited a major genetic risk variant from Neanderthals that increases the risk of severe COVID-19 . In the spring of 2021, they studied this variant in ancient human DNA and observed that its frequency had increased significantly since the last Ice Age. In fact, for a genetic variant inherited from Neanderthals, it has become surprisingly common. Therefore, it may have had a beneficial effect on its carriers in the past. "This major genetic risk factor for COVID-19 is so prevalent that I started to wonder if it actually had any benefit, like providing protection against another infectious disease," Zeberg said.

This genetic risk variant is located in a region of many genes on chromosome 3. Near it are several genes that code for receptors in the immune system. One of these receptors, CCR5, is used by the HIV virus to infect white blood cells. Zeberg found that people who carry this COVID-19 genetic risk variant have fewer CCR5 receptors. This prompted him to test whether these people also had a lower risk of contracting HIV. By analyzing patient data from three major biobanks: FinnGen, UK Biobank and the Michigan Genome Project, he found that carriers of this COVID-19 genetic risk variant had a 27% reduced risk of contracting HIV. "This shows that a genetic variant can be both good news and bad news: If a person gets COVID-19, it's bad news, but if it protects someone from HIV, it's good news," Zeberg said. "

However, since HIV only emerged in the 20th century, reducing the risk of contracting the infectious disease cannot explain why this genetic risk variant of COVID-19 was so prevalent in humans as early as 10,000 years ago. Zeberg concluded, "Today we know that this risk variant of COVID-19 provides protection against HIV infection. But it may be protection against another disease that increased in frequency after the last ice age."