1. Webster RG, Bean WJ, Gorman OT et al (1992) Evolution and ecology of influenza A viruses. Microbiol Rev 56(1):152–179
2. Brown J (2018) Influenza: the hundred year hunt to cure the deadliest disease in history. Simon & Schuster, New York. ISBN-13: 978-1501181245
3. Spinney L (2018) Pale Rider: the Spanish Flu of 1918 and how it changed the world. Vintage, New York. ISBN-13: 978-1784702403
4. World Health Organization: Coronavirus disease (COVID-19). https://www.who.int/health-topics/coronavirus#tab=tab_1. Accessed 25 Oct 2021
5. World Health Organization: tracking SARS-CoV-2 variants. https://www.who.int/en/activities/tracking-SARS-CoV-2-variants/. Accessed 25 Oct 2021