Across the board, if you leave the U.S., you have to obtain a negative COVID-19 test to get back in once your trip is over. American citizens can enter the US from anywhere so long as they have a negative COVID-19 test. Vaccinated travelers still have to test negative twice and unvaccinated travelers have to test negative twice, four days apart, quarantining in between tests. The US has been added to the UK's 'Amber list' of countries; travel is accepted from those countries but with certain rules. UNITED ARAB EMIRATESThe UAE is open to Americans but they have to obtain a negative COVID-19 test and quarantine on arrival.

Source: Daily Mail May 28, 2021 14:06 UTC