After Private David Lewis collapsed and died during a basic training exercise at New Jersey’s Fort Dix on February 4, 1976, an investigation into the 19-year-old’s premature death identified a long-dormant, but notorious killer as the cause.

Blood tests conducted at the Center for Disease Control revealed that Lewis had contracted a type of swine flu thought at the time to be genetically close to the 1918 influenza mislabeled the “Spanish flu,” which claimed the lives of more than 650,000 Americans and as many as 50 million around the globe. Eleven other soldiers at Fort Dix tested positive for swine flu, but recovered—while hundreds more at the base tested positive for swine flu antibodies. The New York Times reported on its front page that the “virus that caused the greatest world epidemic of influenza in modern history—the pandemic of 1918-19—may have returned.”

With the swine flu expected to resurface later that fall, federal officials feared an even deadlier pandemic than that of nearly 60 years earlier. U.S. Secretary of Health, Education and Welfare F. David Mathews projected 1 million Americans would die in the 1976 flu season unless action was taken. Citing the “strong possibility” of a swine flu pandemic, CDC Director David Sencer recommended an unprecedented plan: a mass vaccination of U.S. citizens.

Even though no other swine flu cases had been detected outside Fort Dix, the CDC advocated a better-safe-than-sorry approach. “The administration can tolerate unnecessary health expenditures better than unnecessary deaths and illness,” Sencer wrote in a March 13 memo. When presented with a $135 million plan to prevent a pandemic that could cost billions of dollars and untold lives, President Gerald Ford had little political option, particularly in a presidential election year. “There was no way to go back on Sencer’s memo,” a presidential aide recalled. “If we tried to do that, it would leak. That memo’s a gun to our head.”

Knowing the greatest risk was doing nothing, Ford announced his support of the mass immunization plan at a press conference while flanked by polio vaccine developers Jonas Salk and Albert Sabin. “No one knows how serious this threat could be. Nevertheless, we cannot afford to take a chance with the health of our nation,” the president said. Although CDC officials voiced greater concerns of repeating the 1957 and 1968 flu epidemics, each of which killed approximately 100,000 Americans, administration officials repeatedly raised the specter of 1918.

“The scientists at the time are not saying this is necessarily going to be the Spanish flu redux,” says George Dehner, an associate history professor at Wichita State University and author of Influenza: A Century of Science and Public Health Response. “The way the scientists talked about it was more complex than political officials and the media, who were looking to make the analogy to the Spanish flu.”

Under the National Swine Flu Immunization Program that received bipartisan approval from Congress, the federal government planned to buy 200 million doses of vaccines developed by drug companies and distribute them for free to state health agencies. It would have been the largest immunization campaign in American history, even more ambitious than prior polio vaccination drives.

Problems plagued the program from the start, however. One drug company produced 2 million vaccine doses with the wrong viral strain. Tests could not achieve suitable antibody levels in children. And with the compressed timeframe precluding the typical years of experimentation and clinical trials, insurance companies refused coverage for vaccine makers in the case of inevitable adverse reactions.

With Lewis still the lone swine flu fatality, studies finding the strain less virulent than first thought and the U.S. the only country planning mass vaccinations, Ford’s critics accused him of scaring the public and playing politics with a presidential election looming. “There has always been this undercurrent of doubt about the motivations behind these large-scale programs and whether they were really about making pharmaceutical companies money,” Dehner says. Newsweek was already calling the endeavor the “swine flu snafu” when a mysterious string of deaths stoked fears that the outbreak had already begun.

As the U.S. celebrated its bicentennial summer, a respiratory disease killed 34 people tied to a Philadelphia hotel that had hosted an American Legion convention. Although the cause of what would be known as Legionnaires’ disease was a previously unknown bacterium in the hotel’s air-conditioning system, swine flu was the original suspect. With fears of a pandemic reignited, Congress agreed to indemnify pharmaceutical companies for any adverse vaccine reactions.

Sencer and J. Donald Millar, who directed the CDC’s flu vaccination effort, wrote decades later that the decision had the unintentional consequence of undermining confidence in the vaccine and “ensured that every coincidental health event that occurred in the wake of the swine flu shot would be scrutinized and attributed to the vaccine.”

As public service advertisements urged citizens to “get a shot of protection,” millions of Americans rolled up their sleeves as vaccinations started on October 1. While Ford quipped the shot “may mean a few sore arms,” the press reported the possibility of much worse consequences after three senior citizens died of heart attacks shortly after receiving vaccinations at the same Pittsburgh clinic. While investigations determined no connection between the deaths and the vaccine, a number of states temporarily suspended the program.

Although photographs of Ford receiving a vaccination were distributed in hopes of rallying support, public confidence was further shaken when dozens of vaccine recipients were diagnosed with Guillain-Barré syndrome, a rare neurological disorder causing muscle weakness, tingling in the extremities and paralysis.

Meanwhile, not only had a pandemic yet to appear, but no swine flu cases outside of the Fort Dix cluster had even been reported. Even if there was no connection between the vaccine and Guillain-Barré syndrome, the risk was no longer acceptable. After the vaccination of 45 million Americans—nearly a quarter of the country’s population—the government halted the program on December 16.

Ford lost his re-election bid in the midst of the immunization program that, with the benefit of hindsight, turned out to be unnecessary when a repeat of 1918—or even 1957 or 1968—never materialized. “When lives are at stake, it is better to err on the side of overreaction than underreaction,” wrote Millar and Sencer, who lost his job months later. “In 1976, the federal government wisely opted to put protection of the public first.”