The tables that are used to rank the mutations were created through literature research.
An overview of the papers they are derived from can be found below. The corresponding papers for every single mutation can be found in the source column of the table.
Those are mutations that have been identified previously in the literature as changing the potential of the virus.
Burke, David & Smith, Derek. (2014). A Recommended Numbering Scheme for Influenza A HA Subtypes. PloS one. 9. e112302. 10.1371/journal.pone.0112302.
Ly, Hinh. (2023). Highly pathogenic avian influenza H5N1 virus infection of companion animals. Virulence. 15. 2289780. 10.1080/21505594.2023.2289780.
Brown, Sook & Tseng, Yeu-Yang & Aziz, Ammar & Baz, Mariana & Barr, Ian. (2022). Characterization of influenza B viruses with reduced susceptibility to influenza neuraminidase inhibitors. Antiviral Research. 200. 105280. 10.1016/j.antiviral.2022.105280.
Zaraket, Hassan & Hurt, Aeron & Clinch, Barry & Barr, Ian & Lee, Nelson. (2021). Burden of influenza B virus infection and considerations for clinical management. Antiviral Research. 185. 104970. 10.1016/j.antiviral.2020.104970.
Fukuyama, Satoshi & Kawaoka, Yoshihiro. (2011). The pathogenesis of influenza virus infections: The contributions of virus and host factors. Current opinion in immunology. 23. 481-6. 10.1016/j.coi.2011.07.016.
Those are important regions of the gene like for example Antigenic sites or Receptor-binding sites.
Bush, R & Fitch, W & Bender, Code & Cox, N. (1999). Positive Selection on the H3 Hemagglutinin Gene of Human Influenza Virus A. Molecular biology and evolution. 16. 1457-65. 10.1093/oxfordjournals.molbev.a026057.
Zell, Roland & Groth, Marco & Krumbholz, Andi & Lange, Jeannette & Philipps, Anja & Dürrwald, Ralf. (2020). Novel reassortant swine H3N2 influenza A viruses in Germany. Scientific Reports. 10. 10.1038/s41598-020-71275-5.
Yang, Hua & Carney, Paul & Chang, Jessie & Guo, Zhu & Villanueva, Julie & Stevens, James. (2015). Structure and receptor binding preferences of recombinant human A(H3N2) virus hemagglutinins. Virology. 477. 10.1016/j.virol.2014.12.024.
Burke, David & Smith, Derek. (2014). A Recommended Numbering Scheme for Influenza A HA Subtypes. PloS one. 9. e112302. 10.1371/journal.pone.0112302.