1 WHO. Coronavirus disease (COVID-19) Pandemic, <https://www.who.int/emergencies/diseases/novel-coronavirus-2019> (2020).
2 Li, W. et al. Angiotensin-converting enzyme 2 is a functional receptor for the SARS coronavirus. Nature 426, 450-454, doi:10.1038/nature02145 (2003).
3 Harrison, A. G., Lin, T. & Wang, P. Mechanisms of SARS-CoV-2 Transmission and Pathogenesis. Trends Immunol 41, 1100-1115, doi:10.1016/j.it.2020.10.004 (2020).
4 Cevik, M., Kuppalli, K., Kindrachuk, J. & Peiris, M. Virology, transmission, and pathogenesis of SARS-CoV-2. BMJ 371, m3862, doi:10.1136/bmj.m3862 (2020).
5 Beyerstedt, S., Casaro, E. B. & Rangel, E. B. COVID-19: angiotensin-converting enzyme 2 (ACE2) expression and tissue susceptibility to SARS-CoV-2 infection. Eur J Clin Microbiol Infect Dis, doi:10.1007/s10096-020-04138-6 (2021).
6 Ortiz, M. E. et al. Heterogeneous expression of the SARS-Coronavirus-2 receptor ACE2 in the human respiratory tract. EBioMedicine 60, 102976, doi:10.1016/j.ebiom.2020.102976 (2020).
7 UpToDate. Coronavirus disease 2019 (COVID-19): Clinical features, <https://www.uptodate.com/contents/coronavirus-disease-2019-covid-19-clinical-features?topicRef=126981&source=see_link> (2020).
8 CDC. Demographic Trends of COVID-19 cases and deaths in the US reported to CDC, <https://covid.cdc.gov/covid-data-tracker/#demographics> (2021).
9 UpToDate. Coronavirus disease 2019 (COVID-19): Clinical manifestations and diagnosis in children, <https://www.uptodate.com/contents/coronavirus-disease-2019-covid-19-clinical-manifestations-and-diagnosis-in-children?topicRef=128323&source=see_link> (2021).
10 Brodin, P. Why is COVID-19 so mild in children? Acta Paediatr 109, 1082-1083, doi:10.1111/apa.15271 (2020).
11 Bunyavanich, S., Do, A. & Vicencio, A. Nasal Gene Expression of Angiotensin-Converting Enzyme 2 in Children and Adults. JAMA 323, 2427-2429, doi:10.1001/jama.2020.8707 (2020).
12 Matsuyama, S. et al. Enhanced isolation of SARS-CoV-2 by TMPRSS2-expressing cells. Proc Natl Acad Sci U S A 117, 7001-7003, doi:10.1073/pnas.2002589117 (2020).
13 Saheb Sharif-Askari, N. et al. Airways Expression of SARS-CoV-2 Receptor, ACE2, and TMPRSS2 Is Lower in Children Than Adults and Increases with Smoking and COPD. Mol Ther Methods Clin Dev 18, 1-6, doi:10.1016/j.omtm.2020.05.013 (2020).
14 Abd El-Aziz, T. M., Al-Sabi, A. & Stockand, J. D. Human recombinant soluble ACE2 (hrsACE2) shows promise for treating severe COVID-19. Signal Transduct Target Ther 5, 258, doi:10.1038/s41392-020-00374-6 (2020).
15 Zoufaly, A. et al. Human recombinant soluble ACE2 in severe COVID-19. Lancet Respir Med 8, 1154-1158, doi:10.1016/S2213-2600(20)30418-5 (2020).
16 Nikiforuk, A. M. et al. The Contrasting Role of Nasopharyngeal Angiotensin Converting Enzyme 2 (ACE2) Expression in SARS-CoV-2 Infection: A Cross-Sectional Study of People Tested for COVID-19 in British Columbia, <https://www.medrxiv.org/content/10.1101/2020.11.23.20237206v3> (2020).