1. Centers for Disease Control and Prevention. Variants of the virus. https://www.cdc.gov/coronavirus/2019-ncov/variants/index.html (2021).
2. Centers for Disease Control and Prevention. SARS-CoV-2 variant classifications and definitions. https://www.cdc.gov/coronavirus/2019-ncov/variants/variant-classifications.html (2021).
3. Centers for Disease Control and Prevention. CDC data tracking. https://covid.cdc.gov/covid-data-tracker (2020).
4. Michael, E. & Jordan, H. COVID-19 economic crisis. https://carsey.unh.edu/COVID-19-Economic-Impact-By-State (2021).
5. The New York Times. Coronavirus (Covid-19) Data in the United States. https://github.com/nytimes/covid-19-data (2021).