Down syndrome (sometimes called Down's syndrome) is a condition in which a child is born with an extra copy of their 21st chromosome - hence its other name, trisomy 21.
This causes physical and mental developmental delays and disabilities.
"Although the down syndrome was not specifically mentioned on official lists of conditions that put people at increased risk, the condition is associated with immune dysfunction, congenital heart disease, and pulmonary pathology," said study author from the UK.
Therefore, it may be an unconfirmed risk factor for severe Covid-19, the study, published in the Annals of Internal Medicine, reported.
For the findings, researchers from the University of Oxford, the University of Nottingham and the University College London studied a cohort of 8.26 million adults through a 'QResearch' database to evaluate if the down syndrome is a risk factor for death from Covid-19.
The authors found an estimated a 4-fold increased risk for Covid-19-related hospitalisation and a 10-fold increased risk for Covid-19-related death in persons with Down syndrome.
"We are unaware of the effects of down syndrome on Covid-19 outcomes being reported elsewhere yet during this pandemic," the study authors wrote.
They stressed this novel evidence should be used by public health organisations, policymakers, and health care workers to strategically protect vulnerable individuals.