Pääbo is known as one of the founders of paleogenetics, a discipline that uses the methods of genetics to study early humans and other ancient populations. In 1997, Pääbo and colleagues reported their successful sequencing of Neanderthal mitochondrial DNA (mtDNA), originating from a specimen found in Feldhofer grotto in the Neander valley. In 2020, Pääbo determined that more severe impacts upon victims including the relative incidence of the necessity of hospitalization requirements, and vulnerability to the COVID-19 disease has been associated via DNA analysis to be expressed in genetic variants at chromosomal region 3, features that are associated with European Neanderthal heritage. That structure imposes greater risks that those affected will develop a more severe form of the disease. The findings are from Pääbo and researchers he leads at the Planck Institute and the Karolinska Institutet. This admixture of modern human and Neanderthal genes is estimated to have occurred roughly between 50,000 and 60,000 years ago in Southern Europe.