“The Centers for Disease Control and Prevention (CDC) has issued a Level 4 Travel Health Notice for France due to Covid-19, indicating a very high level of Covid-19 in the country.”
In practice this will not have a big effect at present, since France allows only essential travel from the USA and arrival numbers are very low.
However French president Emmanuel Macron has said that he hopes to open up travel to vaccinated Americans by the summer.
The State Department's travel warning is advisory, but travel to a Level 4 destination can invalidate travel insurance.
Previously, the State Department listed 34 of about 200 countries worldwide with the “Do Not Travel” warning, and has since increased the number to 150 countries based on the recommendations of the CDC.