Holidaymakers are a loyal bunch. Crowds of luggage-toting Americans have packed airports this summer despite pricier flights and hotels. More than 2mn people have passed through US airport screenings every day since early June. On some days, volumes have surpassed pre-pandemic levels, according to the Transport Security Administration.

One group reluctant to join in the fun is investors. Stock prices for the four biggest US airlines by revenues — Delta, American Airlines, United and Southwest — have dropped between a fifth and a third since late April despite the travel boom.

Some of this bearishness is justified. Staff shortages have forced airlines to cancel thousands of flights. Jet fuel costs have doubled in the past year. A recession could hurt travel demand.