Ahmed Ali D, Ahmed Ali I, Devi U, Maheshwari C. The application of topical oxygen therapy in the treatment of diabetic foot ulcers; A systemic review. HPHR. 2022;67.
COVID-19 is a life-threatening disease and many risk factors have been identified  but its association with down syndrome is still unknown or very less data is available regarding it.
De Cauwer H et al (Dec 2020)  was the first study that reported the association of COVID-19 with down syndrome in adult patients. It included 4 Patients with DS and COVID-19. All showed severe COVID-19 and needed hospital admission. Later on, many studies ,,, conducted in this regard showed DS was associated with severe COVID-19 in adults.
Until mid-2020, the occurrence of COVID in pediatric DS patients was unknown. In Dec 2020, case reports published by Kantar A et al  showed the occurrence of severe COVID-19 in children. These were the first cases reported that showed the association of COVID with DS in children.
Down syndrome leads to severe immune dysregulation.  Scientists are investigating the exact mechanism behind the dysregulation of the immune system caused by trisomy 21 or down syndrome but still, the research on it is going on. In DS, chromosome 21 activates multiple genes which cause hyperactivity of the immune system. Chromosome 21 encodes the following immune regulators: interferon (IFN) receptors, (IL)-10, IL-22, and IL-26.  Immune and non-immune cells are sensitive to IFN and many studies report that in the absence of any infection there is still hyperactivity of T cells due to TFN in DS patients.  IFN response which is involved in the antiviral response is vigorous in DS patient and lead to cytokine storm. [14-15] Recent studies showed that COVID infections are driven by an exacerbated immune response to the virus, leading to cytokine storm, acute respiratory distress syndrome, thromboembolic processes, and multi-organ failure. 
the Chilean Ministry of Health requested advice from the Genetics Branch of the Chilean Society of Pediatrics which reported that DS children and adults are a vulnerable group related to COVID and should be prioritized for vaccination. 
The limitation of this systemic review is that it includes the conclusion from fewer studies related to the topic and small sample size is included in the studies as very limited data is available on the above topic. More research is required on this topic and further clarification is needed on this topic.
All studies showed that Down syndrome is associated with severe COVID and can lead to hospitalization and complications. Adults and children with COVID and down syndrome are more vulnerable and should be prioritized for vaccination.
1.Faundes V, Pardo R, Cammarata-Scalisi F, Alarcon P, Lay-Son G, San Martin E. Consenso de la Rama de Genética de la Sociedad Chilena de Pediatría sobre priorización de personas con Síndrome de Down y otras condiciones poco frecuentes en la Campaña de Vacunación COVID-19 [Consensus of the Genetics Branch of the Chilean Society of Pediatrics on the prioritization of people with Down syndrome and rare diseases for vaccination against SARS-CoV-2]. Andes Pediatr. 2021 Apr;92(2):309-315. Spanish. doi: 10.32641/andespediatr.v92i2.3716. PMID: 34106172.
2.Vita S, Di Bari V, Corpolongo A, Goletti D, Espinosa J, Petracca S, Palmieri F, Nicastri E; INMI COVID-19 study groups. Down Syndrome patients with COVID-19 pneumonia: A high-risk category for unfavourable outcome. Int J Infect Dis. 2021 Feb;103:607-610. doi: 10.1016/j.ijid.2020.11.188. Epub 2020 Nov 30. PMID: 33271290; PMCID: PMC7703224.