As I read through Icelandair's Covid info, I am getting the impression that to board the flight from the US to France, you just need your CDC card, you only need a PCR test result if you are unvaxxed or planning a layover in Iceland. Anyone with recent experience?
The French entry requirements have been stable for some time now, those vaccinated need only the CDC card.
Entry into Iceland may be different, I have no specific references for entering countries other than France.
On Icelandair's website I found the following regarding "transit passengers" (i.e. those who change flights at Keflavik airport), updated September 2:
Do you need a negative test before boarding? Yes, transit passengers who are vaccinated or have recovered from COVID must show a certificate of negative COVID-19 test before boarding an aircraft to Iceland, together with their certificate of vaccination or previous infection*. The COVID-19 test must be taken within 72 hours of departure. Results from PCR and rapid antigen tests are accepted. Self-tests are not accepted. For passengers flying from England, NHS tests are not accepted.
For more detailed information of Iceland's regulations you can check covid.is. I don't know your flight dates--but I do know that the rules often change, so keep checking prior to your trip. Happy travels!
Den, thank you so much, I somehow missed that in my rooting around on their website. Merci!!