A phenomenon that has underpinned the COVID-19 pandemic is the range in severity of symptoms. While millions have tragically lost their lives, many people are asymptomatic. Although COVID-19 symptoms can vary by age, gender and ethnicity, these factors alone do not explain this disparity.

Scientists have been investigating this in the hope of identifying an effective way to treat severe COVID-19. Using different methods of investigation, two pre-prints have reported that a protein called OAS1 influences COVID-19 outcomes. The studies, which have not yet undergone peer review, describe a protective variant in OAS1 that is inherited from Neanderthals.

OAS1 activates enzymes in our cells that are responsible for RNA degradation. SARS-CoV-2, the virus responsible for COVID-19, is an RNA virus, and therefore this protein could potentially serve as part of the immune response against it. The same variant was found to be protective against SARS-CoV, the virus responsible for the 2002-2004 SARS outbreak.

Different people have different forms of proteins due to genetic variation. The Neanderthal variant of OAS1 has greater anti-viral activity than other isoforms. The variant was introduced into the European population via gene flow between Neanderthals and the ancestors of present-day humans. Neanderthal ancestry makes up 1.5-2.1% DNA in people outside of Africa, and many of these genes have been selected for over time.

This is not the first instance of Neanderthal variants influencing COVID-19 outcomes. A study published in Nature in September 2020 detailed a stretch of DNA on chromosome 3, identical to the Neanderthal genome, that tripled the risk of developing severe COVID-19.