Airlines are touting deep cleaning and hospital-grade air filters. American said it had teamed with Vanderbilt University Medical Center on health and cleaning matters and will begin asking customers June 30 during the check-in process to certify they have been free of COVID-19 symptoms for 14 days.

U.S. passenger numbers have rebounded from lows reached in April, but there is growing concern about the impact of a fresh spike in coronavirus cases in many U.S. states, including Texas, where American is based.