So saying there is "no basis" is a bit rich. There may still be uncertainty.
Edit: this (just googled) article cites Diamong Princess to lead to an estimate of 0.5% death rate https://www.sciencenews.org/article/coronavirus-outbreak-dia... (the percentage of deaths on the DP was higher, but the passengers were also comparatively old on average).
Edit 2: lol for the downvote. What the fuck?
Edit 3: about the study in Germany https://www.theblaze.com/news/german-study-shows-coronavirus... (don't know "The Blaze", but if you care, you can google for better sources - google for "Streeck").
Edit 4: Theodore Roosevelt carrier https://en.wikipedia.org/wiki/2020_coronavirus_pandemic_on_U...