Hi - So yes, I actually called Cunard TWICE and they assured me it was fine and americans can use their CDC original cards, but they won't give it to me in writing.
The email I'm referring to came today with the title "
Important information for your upcoming voyage
Here is the relevant paragraph that has sent me into a complete panic:
Covid‑19 vaccination and testing requirements
Please visit our website for the most up-to-date Covid-19 vaccination and testing requirements for your voyage.
You’ll be required to show proof of your vaccination status (and booster where applicable) at the terminal prior to boarding, which will also be checked against your photo ID. Please note, that the record card that is given out at the time of vaccination will not be accepted as proof of your vaccination status. Unfortunately, failure to provide proof of vaccination at the terminal will result in denial of boarding at your own expense. You may also be required to show proof of a negative Covid‑19 test at the terminal.