The United States has joined a string of other countries requiring international arrivals to take a pre-flight COVID test as it attempts to slow the introduction of new variants. A health order issued by the Centers for Disease Control prohibits entry to the US of any arriving aircraft passenger who does not have a negative result from a test taken up to 72 hours prior to departure. Passengers who have previously had COVID-19 must provide written or electronic documentation showing they recorded a positive viral test result and a letter from a licensed health care provider or public health official showing they are fit for travel. READ: More airlines could fail as forward bookings stall. The order applies from January 26 to US citizens and foreigners over the age of two. Anyone who does not meet the requirements will be denied boarding. “Testing before and after travel is a critical layer to slow the introduction and spread of COVID-19. This strategy is consistent with the current phase of the pandemic and more efficiently protects the health of Americans,’’ the CDC said in the health order. “Variants of the SARS-CoV-2 virus continue to emerge in countries around the world, and there is evidence of increased transmissibility of some of these variants. "With the US already in surge status, the testing requirement for air passengers will help slow the spread of the virus as we work to vaccinate the American public.” Passengers will need to show the documentation initially to an airline but must also retain it and produce it on request to any US government official or “cooperating state or local public health authority”. The onus will be on airlines and other aircraft operators to verify that every passenger two years or older is cleared for travel and that they have the necessary documentation. International travel has already been devastated by tightening COVID-19 restrictions being imposed worldwide and the International Air Transport Association expects problems to continue through the first half of 2021. The US move follows similar actions by countries such as Germany, Japan, Australia, New Zealand and Canada. The CDC said it had delayed the introduction of the requirement to allow passengers and airlines to adapt but CDC director Robert Redfield warned it did not eliminate all risk. However, when combined with other precautions such as a period of staying at home, masks and social distancing, "it can make travel safer, healthier, and more responsible by reducing spread on planes, in airports, and at destinations”. US carriers are already reacting to the move and Delta Air Lines said it had proactively issued a fare difference waiver for customers rebooking international tickets on or before January 12. The US has the highest number of infections and deaths in any country with more than 22 million cases and 375,000 deaths.