Within 3 days of departing the UK to return to the US, take another COVID test. This is required by the US CDC according to this link, and both PCR and Rapid Antigen tests are acceptable. I am planning to walk into an NHS location near the EA conference venue (like this) and get a free test. You don’t have to be a UK citizen to get free tests from the NHS (link).
My understanding is that you should not be using the free NHS test for travel and should instead book a private test, which is possible across London and at airports on the day of your flight. See the travelling abroad section of this NHS page. More practically, I think you only get a text message confirming your result from the NHS tests and this is not sufficient documentation for the CDC requirements.
What information must be included on the test result?
A test result must be in the form of written documentation (paper or electronic copy). The documentation must include:
1 . Type of test (indicating it is a NAAT or antigen test)
2. Entity issuing the result (e.g. laboratory, healthcare entity, or telehealth service)
3. Specimen collection date. A negative test result must show the specimen was collected within the 3 days before the flight. A positive test result for documentation of recovery from COVID-19 must show the specimen was collected within the 3 months before the flight.
4. Information that identifies the person (full name plus at least one other identifier such as date of birth or passport number)
5. Test Result
My understanding is that you should not be using the free NHS test for travel and should instead book a private test, which is possible across London and at airports on the day of your flight. See the travelling abroad section of this NHS page. More practically, I think you only get a text message confirming your result from the NHS tests and this is not sufficient documentation for the CDC requirements.