This analysis of large-scale population-level UK primary care data identified that people with DS had a significantly increased likelihood of receiving a COVID-19 diagnosis compared to controls (OR = 1.35; 95% CI 1.23–1.48), and this was not entirely explained by multimorbidity. We found that susceptibility to COVID-19 diagnosis across the cohort was associated with specific comorbidities including anxiety disorders, other chronic inflammatory conditions/other autoimmune conditions, dementia, depression, epilepsy, hypertension, asthma and chronic respiratory disease excluding asthma. In particular, people with DS and a chronic respiratory disease diagnosis were significantly more susceptible to COVID-19 (OR = 1.71; 95% CI 1.20–2.43). However, this did not remain significant when controlling for exposure through living situation in a smaller sub-sample of patients with data available on living situation.
Our findings of an interaction between chronic respiratory conditions in DS and risk of COVID-19 diagnosis may indicate a common mechanism for increased risk for respiratory conditions in general in DS individuals, or alternatively that existing respiratory vulnerability (excluding asthma) may be associated with increased susceptibility to infection with SARS-CoV-2. DS is associated with certain anatomical differences, facial and airway tract features that may increase risk for respiratory infections, such as macroglossia, a narrow nasopharynx and a shortened palate, further complicated by generalised hypotonia.21 These may be associated with increased risk for ear, nose and throat infections22 and obstructive sleep apnoea.23 Furthermore, a higher prevalence of congenital cardiac anomalies and pulmonary hypertension24 may further increase the risk for respiratory infections in people with DS.
Ultimately, respiratory infections are a significant source of increased morbidity and mortality in children and adults with DS.25 Approximately 40% of children and young adults (aged < 30 years) with DS experience at least one episode of pneumonia.26 Pneumonia was associated with higher risk of inpatient mortality when adjusting for age, gender and ethnicity for adults with DS compared to controls using data from the UK.27
Type 1 interferons (IFNs) help to regulate the activity of the immune system. Trisomy 21 is characterised by enhanced IFN-1 signalling due to overexpression of IFN genes on chromosome 21 (IFNAR1, IFNAR2 and IFNGR2). The effect on respiratory infections are difficult to predict, though may have both positive and negative effects by enhancing anti-viral response and overactivation of the immune system with risk for a cytokine storm.7 Individuals with DS may also have reduced lymphocyte numbers.28 Immune dysregulation has been proposed to be a syndromic feature,29 and the cell-mediated immunodeficiency combined with impaired antibody response to pathogens may explain the increased risk for and mortality associated with pneumonia and other respiratory diseases in children with DS.
Given the biological risk associated with increased viral entry, individuals with DS may also have a particular predisposition for viral respiratory infections in general, rather than specifically for SARS-CoV-2. TMPRSS2 belongs to the type II transmembrane serine protease family and is commonly expressed in epithelial tissues such as those lining the upper airways, bronchi and lung.30,31 Influenza viruses and other coronaviruses all critically depend on TMPRSS2 for viral activation and cellular infection.31,32 Viruses such as influenza virus, respiratory syncytial virus (RSV) and parainfluenza virus likely account for most of the respiratory infections in DS,22,33 and those with congenital cardiac conditions or pulmonary hypertension may be particularly vulnerable.
Obesity is a common comorbidity in DS, and associated with increased disease severity when diagnosed with COVID-19 in the general population, probably through its association with decreased lung reserve volume and capacity, as well as reduced pulmonary function in bed-bound patients. Obesity is also associated with higher levels of inflammatory cytokines, which may contribute to higher mortality rates in obese individuals with COVID-19.34 In the present study, obesity was not associated with increased susceptibility to COVID-19 when adjusting for other comorbidities. This suggests that the increased risk associated with obesity may be related to complications and treatment outcomes rather than susceptibility to infection. Additionally, congenital heart disease may be associated with higher risk for hospitalisation in those with COVID-19 infection,10 but although 35% of DS participants had a diagnosis of congenital heart conditions in our study, it was not associated with increased susceptibility to infection.
Our data and other research suggest that individuals with DS are particularly at risk for COVID-19 and other respiratory infections. Our data further emphasises the need to prioritise individuals with DS for COVID-19 vaccination. They should also be prioritised for surveillance of respiratory infections during high-risk periods,35 and for implementing additional safety measures during pandemics. This may include preventing and rapidly containing transmission in long-term care facilities, providing support to caregivers on close monitoring and safe care, and identification of symptoms that may indicate the need for assessment for admission to hospital. Active medical management to ensure access to oxygen therapy and drugs such as steroids and antibiotics when needed could prevent complications and hospital admissions. There may also be a rationale for offering pneumococcal vaccine in addition to flu vaccine to children and adults with DS. Other preventative measures include management of comorbidities such as obesity and treatment of sleep apnoea.36 Future studies on the contribution of TMPRSS2 triplication and developing therapies that may be particularly relevant to DS are needed.
This is the largest study to date of COVID-19 in individuals with DS, including nearly 9000 DS individuals, of whom 651 were diagnosed with COVID-19. We included data from the whole of 2020 and part of 2021, thus covering the initial and subsequent waves of the pandemic in the UK. Nevertheless, differential access to testing might have been a potential source of bias due to limited access to tests during the first wave of the pandemic.37 Whilst the probability of an infected person receiving a test might have been variable over time, it is unlikely to account for differences in rates between individuals with DS and general population controls since it affected all patients and GPs across the UK. It is possible that those with symptomatic infections were more likely to be tested and recorded with an infection by their primary care physicians than asymptomatic cases. Whether people with DS are less likely to experience asymptomatic infections is currently unknown. Our exploratory sub-analysis examining the impact of living situation on COVID-19 diagnosis found that living in residential or care settings may increase the likelihood of COVID-19 diagnosis. This finding is consistent with the excess mortality and infection rates reported in the UK38 and internationally39 for those living in residential or care settings. Whilst living situation was an important risk factor for COVID-19 diagnosis, this analysis was only conducted in 10% of the total sample with living situation data available and only 2.3% (800/34,724) of controls had data on this variable. Therefore, the interaction between living situation and chronic respiratory disease in those with DS could not be fully examined, and future studies with better recording of living situation data are needed. Further, it is not yet clear how multimorbidity and health-seeking behaviours may have influenced COVID-19 diagnosis. Multimorbidity is associated with increased primary care use40 which may have increased the likelihood of patients consulting with their GP for COVID-19 symptoms. Therefore, the relationship between COVID-19 diagnosis and multimorbidity warrants further investigation.
Individuals with DS have both increased susceptibility to COVID-19 infection and are more likely to experience severe outcomes. Susceptibility to COVID-19 is increased during peaks of the pandemic and associated with health comorbidities in individuals with DS, particularly chronic respiratory conditions. Although lockdowns and the associated measures to wear masks and social distancing appeared to have an effect in reducing the initial wave of the pandemic, it did not seem to prevent excess infections in DS individuals during the 2nd wave in the autumn winter of 2020, suggesting that these measures were not fully utilised for this group, or else that additional safeguards may be required. This has important public health implications to manage risk during the ongoing SARS-CoV-2 pandemic, as well as to manage the risk associated with respiratory infections in people with DS. Individuals with DS who have underlying lung conditions should take extra care to safeguard themselves during viral pandemics, and our findings suggest a strong rationale for them to be prioritised for vaccination with COVID-19, influenza and pneumococcal vaccines.