Dr. Patrice Harris, the former president of the American Medical Association and the chief executive of eMed, which sells at-home coronavirus tests to travelers and Delta Air Lines, said the “it’s-too-complicated” argument is a poor excuse. “The key is making the right thing to do, the easy thing to do,” she said.

Hawaii is the one state that requests proof of vaccination or a negative test from domestic visitors. In order to avoid quarantine, travelers can upload an image of their C.D.C.-issued vaccination card or a negative coronavirus test to the state’s Safe Travels system. The system has gone through several iterations: Early on, checking test results created terrible lines at airports and caused havoc for travelers with connecting flights said Peter Ingram, the chief executive of Hawaiian Airlines.

However, Mr. Ingram was more positive than other executives interviewed about expanding such a system across the country. “I wouldn’t say that it can’t possibly work,” he said. One of his primary concerns is how to deal with acceptable exceptions to a vaccine mandate.

“Who is going to be the adjudicator?” he asked.

“It’s safe on board, safer than an operating room,” said Deborah Flint, the chief executive of Greater Toronto Airports Authority, during one of the air summit’s panels.

This line comes from a widely recognized study, conducted by the Defense Department and published last October, which found that air circulation systems in two types of large Boeing aircraft were even better at filtering out airborne particles than the filtration systems recommended for most hospital operating rooms.

Other research has also reinforced that air in a typical cabin is refreshed every two to three minutes, inhibiting the transmission of the coronavirus. But the risk of transmission increases when passengers fail to properly wear masks, Dr. Lin H. Chen, the former president of the International Society of Travel Medicine noted. (A case study published last week reinforced this point: One person not wearing a mask on a two-hour domestic flight in March 2020 in Japan, seems to have infected at least 14 other people despite a modern air filtration system.)

Even with a federal mask mandate, some people while on board do and will refuse to wear masks properly. Others cannot wear them for medical reasons, because they are too young or because they are eating or drinking. But even assuming everyone age 2 and above — airlines’ standard age for mask requirements — is properly wearing one, experts still don’t know how new variants are changing the equation, said Dr. David Freedman, a professor of infectious diseases at the University of Alabama at Birmingham. “Delta is much more transmissible,” he said.