All of the included systems facilitate search or exploration over the COVID-19 literature, though some feature more specific text understanding tasks such as summarization, QA and claim verification. To facilitate a comparison between systems, we provide the following in Table 2: (i) data used, (ii) models/methods used or implemented by each system and (iii) supported user interface features. In some cases, information is not provided or could not be found about the data or models/methods used; we have indicated this using ‘–’.