The COVID-19 pandemic prompted immense investigation of the SARS-CoV-2 virus. Rapidly, accurately, and easily interpreting generated data is of fundamental concern. Ontologies – structured, controlled, vocabularies – support interoperability, and prevent the development of data silos which undermine interoperability. The Open Biological and Biomedical Ontology Foundry serves to ensure ontologies remain interoperable through adherence by its members to core ontology design principles. For example, the Infectious Disease Ontology (IDO) Core includes terminological content common to investigations of all infectious diseases. Ontologies covering more specific infectious diseases, in turn, extend from IDO Core, such as the Coronavirus Infectious Disease Ontology (CIDO). The growing list of virus specific IDO extensions has motivated construction of a reference ontology covering content common to viral infectious disease investigations: the Virus Infectious Disease Ontology (VIDO). Additionally, the present pandemic has motivated construction of a more specific extension of CIDO, covering terminological content specific to the pandemic: the COVID-19 Infectious Disease Ontology (IDO-COVID-19). We report here the development of VIDO and IDO-COVID-19. More specifically, we examine newly minted terms for each ontology, showcase reuse of terms from existing OBO ontologies, motivate choice-points for ontological decisions based on research from relevant life sciences, apply ontology terms to explicate viral pathogenesis, and discuss the annotating power of virus ontologies for use in machine learning projects.