Covid-19 testing within 72 hours of departure cuts exposure risk on a flight to less than 0.1 percent, according to a study conducted by Delta Air Lines, the Mayo Clinic and the Georgia Department of Health.
The study used customer data on Delta's Covid-tested flights to Rome, which began in late 2020. Passengers in the study, after already being tested prior to departure, were tested again with a rapid antigen test after going through security in Atlanta and New York before departure. Any passengers who tested positive were then subjected to a rapid molecular test. If both tests were positive, passengers were not allowed to board, but passengers who tested positive on the rapid antigen test but negative on the rapid molecular test were still allowed to board. Upon arrival in Italy, passengers again were tested with rapid antigen tests, followed up with rapid molecular tests if the first came back positive.
Of the nearly 10,000 passengers who underwent the testing, only four, or 0.04 percent, tested positive on both the antigen and molecular tests in the U.S., according to the study. By comparison, the average community infection rate was about 1.1 percent during the time of the study. Only one additional passenger tested positive on both tests upon arrival in Italy.
Those results indicate that the 72-hour testing requirement "significantly mitigates the risk of Covid-19 exposure and transmission during airline travel," Delta chief health officer Henry Ting said in a statement. The additional airport testing, meanwhile, "is unlikely to add safety alongside other mitigation efforts" such as mask requirements, given the small percentage of positive tests, according to Delta.
"When you couple the extremely low infection rate on board a Covid-19-tested flight with the layers of protection on board including mandatory masking and hospital-grade air filtration, the risk of transmission is less than one in one million between the United States and the United Kingdom, for example," according to Ting. "These numbers will improve further as vaccination rates increase and new cases decrease worldwide."