In this time of crisis, would the journals Nature and Science prioritize papers about COVID-19?
Absolutely. Journals are ways of disseminating scientific information, and they do take into account what is of current interest.

More specifically, however: Both Science and Nature do not just publish scientific articles, but also commentary and news stories. For example, in Science they are in the "News" and "Perspectives" parts of the magazine, and they definitely cover current events. As, if I may add, they should.