The International Committee on Taxonomy of Viruses (ICTV) is responsible for classifying viruses and they use a bunch of different criteria, such as chemical ch

The International Committee on Taxonomy of Viruses (ICTV) is responsible for classifying viruses and they use a bunch of different criteria, such as chemical characteristics, structure (e.g. look at Covid-19 vs a bacteriophage), type of nucleic acid, mode of replication, host organisms, and the types of diseases they cause. They also group them based on common ancestors. In other words, it becomes a new species when there's a change to the phenotypic traits above.