From the Open Citations Blog Post:
We are excited to share that COCI, the OpenCitations Index of Crossref open DOI-to-DOI citations, was on 12 May 2020 extended with more than 47 million additional citations, and has reached a total number of more than 702 million DOI-to-DOI citation links between more than 58 million bibliographic entities.
The citations added in this the fifth release of COCI came from the most recent Crossref dump downloaded on 22 April 2020, which includes the references of the articles deposited in Crossref between 4 October 2019 and 4 April 2020. Such updates to COCI will now occur regularly at bimonthly intervals.
As a consequence, COCI now contains 702,772,530 citations, and also includes publications about the COVID-19 pandemic. We will use this new release of COCI to update the Coronavirus Open Citations Dataset, the second release of which will include details about these additional references and publications.