1. Centers for Disease Control and Prevention, USA https://www.cdc.gov/coronavirus/2019-ncov/about/index.html
2. Government of Canada https://www.canada.ca/en/public-health/services/diseases/coronavirus-disease-covid-19.html
3. Mayo Clinic, USA https://www.mayoclinic.org/diseases-conditions/coronavirus/symptoms-causes/syc-20479963
4. National Health Service, UK https://www.nhs.uk/conditions/coronavirus-covid-19/
5. National Institute for Clinical Care and Excellence (NICE), UK. Coronavirus - COVID-19. 2020 https://cks.nice.org.uk/coronavirus-covid-19#!topicSummary