For 15 years, the U.S. government has been pressing airlines to prepare for a possible pandemic by collecting passengers’ contact information so that public-health authorities could track down people exposed to a contagious virus.

The airlines have repeatedly refused, even this month as the coronavirus proliferated across the United States. Now the country is paying a price.

As the coronavirus spread into the United States this year, the federal government was not able to get in touch with or monitor airline passengers who might have been exposed to the disease or were carrying it into new communities.

Officials at the Centers for Disease Control and Prevention and the Department of Health and Human Services have spent years warning airlines that they have complete contact information for only about half of their passengers, those who book flights directly through the airlines as opposed to third-party ticketing websites like Travelocity. During the Ebola outbreak in 2014, for example, the scarcity of contact information handicapped the CDC as it tried to reach Americans who might have been exposed to the virus, according to three government officials.

But airline executives and lobbyists have protested that it would be expensive and time-consuming for them to start collecting basic information like email addresses and phone numbers for all passengers.

The lobbying has worked. Over the past 15 years, the industry has beaten back proposed rules and legislation that would have compelled airlines to collect contact information before passengers board flights. Even last week, as Congress approved tens of billions of dollars in aid to the industry, the airlines helped derail an attempt by the Trump administration to require them to start compiling such information.

While the government has access to flight manifests showing who is on board each flight, and where they sit, there is sufficient contact information for only about half of the passengers on any given flight. If a passenger later tested positive for the coronavirus, government officials said, they would struggle to get in touch with people who sat near that passenger to see if they, too, had been infected.

Current and former officials at the CDC said in interviews that the lack of information compromised their ability to perform contact tracing of airline passengers, a tactic that helped combat the coronavirus in countries like South Korea.

“Contact tracing is really hard. You have to find people, build their trust and keep in touch with them,” said Dr. Thomas Frieden, who ran the CDC during the Obama administration. “This is the bread and butter of public health, and every little bit you can do to give you a lead helps.”

The industry’s battle against collecting more information for the government dates back to 2005, when health officials were assessing their response to the SARS outbreak.

By the time of the Ebola outbreak in 2014, there still was no system in place. When the CDC asked airlines for more information to help find passengers who were sick or had potentially been exposed to Ebola, the airlines complained about “the burden and the privacy concerns” of providing that data, Frieden said.

“They were vehement about it,” he said.

In 2016, the CDC wanted to mandate by law that air carriers collect and share such information.

The industry again protested. Lobbyists from Airlines for America, a powerful trade association, noted that about half of all tickets were booked through sites such as Expedia and Travelocity. Those companies, which compete against airlines for customers, are loath to share passenger data with rival companies that might try to steal their business.

In an October 2016 letter to the CDC and Health and Human Services, Douglas Lavin, an executive at the International Air Transport Association, another airline trade group, wrote that the “CDC has not adequately accounted for the industry burden and cost for collecting these new data elements.” The letter was signed by five airline lobbying groups.

Then, in January, the coronavirus arrived by plane in Seattle.

In a series of tense conference calls that began in January, CDC officials told Lavin and an Airlines for America lobbyist, Sharon Pinkerton, that the agency was planning to issue an emergency rule that would compel the airlines to collect and share detailed passenger data, according to five people who were on the calls. The CDC argued that such resources were crucial for them to contain the crisis.

Airline officials responded that it would be impossible for them to retool their computer systems, some of which were based on technology developed in the 1970s, fast enough to aid the government’s fight against the coronavirus. They presented two alternatives: Airlines could hand out paper forms for passengers to fill out and then the government could pay to have the data entered into databases. Or the airlines could quickly develop an app that the government could use to require that travelers provide accurate information in order to enter the United States.

“We have said we will do this, but it’s going to take 12 months,” Pinkerton, the airline lobbyist, said in an interview. “But we think there are better ways to do this.”

The airlines found a sympathetic ear inside the Trump administration, including among senior officials at the Federal Aviation Administration. On conference calls with other government officials, Dan Elwell, the deputy FAA administrator, made the case that it would be extremely difficult for airlines to redesign complex technical systems to gather the passenger information, according to two people with knowledge of the calls. Before joining the FAA, Elwell worked for two years as an executive at Airlines for America.

On Feb. 12, the Health and Human Services Department issued a temporary rule requiring airlines to gather detailed passenger data. The rule expires once the coronavirus pandemic ends.

But the airlines said it would take a year for them to change their computer and other systems to enable them to start collecting the information, and in the meantime they are fighting to undo the rule. In a March 13 letter to the CDC and the Health and Human Services Department, lobbyists from Airlines for America and the International Air Transport Association said the airlines and travel agents would have to spend $164 million to buy more airport check-in kiosks, installing new computers and hiring more gate agents, among other costs.

“The CDC is using the COVID-19 outbreak to make airlines spend hundreds of millions of dollars to create new systems or modify old systems,” the lobbying groups wrote in the letter, which was also signed by the Regional Airline Association and the National Air Carrier Association.

As Congress rushed to pass a huge stimulus bill last week, the government’s top health officials tried again to permanently solve their contact-tracing problems. In discussions days before the bill was pushed through, they asked Republican Senate staff members to include language that would require airlines to digitally collect traveler data in exchange for receiving the largest government bailout in history.

The CDC was rebuffed. Senate aides were concerned about the privacy implications of such a requirement and didn’t want to impose extra burdens on an already distressed industry.

They also knew that two key senators — Ted Cruz, R-Texas, and Kyrsten Sinema, D-Ariz. — had questioned the idea. At a hearing in March, Sinema presented a letter written by the Airlines for America lobbying group, which suggested using paper forms or an app. In March, the two senators wrote a letter to Vice President Mike Pence saying that they favored a government-run app.

Sinema — who along with Cruz sits on the Senate Commerce Committee, which oversees the airline industry — received more money from the Airlines for America lobbying group than any other member of Congress in 2018, according to the Center for Responsive Politics. Cruz was among the top recipients of money from Delta and American Airlines that same year.

Sinema said in a statement that she had “worked across the aisle for weeks to convince the federal government to adopt an app quickly to make contact tracing at all ports of entry a reality.”

Lauren Aronson, a spokeswoman for Cruz, said in a statement that “while Sen. Cruz understands the importance of contact tracing, thrusting an unfunded mandate that requires all the carriers to rework their entire IT systems, at a time when the carriers are hurting badly, was not appropriate or effective.”

On Friday, President Donald Trump signed a bailout bill that awarded the airline industry more than $60 billion in taxpayer funds. It did not require airlines to collect new information about passengers.