In February 2009, a spike in influenza cases was detected in hospitals around Mexico City. Mexican government officials sent samples of throat cultures from patients to the US Centers for Disease Control (CDC) and the Canadian National Laboratory in Winnipeg, whose scientists found a new version of the H1N1 influenza virus, named for the type of hemagglutinin and neuraminidase molecules on its surface that enable it to spread within the body.

The discovery of what came to be known as “swine flu”—because pigs were the original source of the virus—aroused enormous concern in public health circles. The 1918 flu pandemic that killed tens of millions of people globally was also caused by an apparently new version of H1N1 influenza. Although other H1N1 viruses had been circulating in US populations for more than thirty years,1 the Mexican virus looked different and at first seemed to be especially aggressive. Soon the World Health Organization (WHO) began raising the alarm. Two billion people—one third of the global population—could contract the disease, the agency warned, and millions might die. World Bank economists suggested that the total cost of such a pandemic—counting lost business and increased health spending—could even reach 4.8 percent of global GDP.2

Panic spread throughout the world. In Mexico schools and offices were closed, flights were canceled, and the country lost $2.2 billion within a few weeks.3 In the UK, the government’s swine flu website received 2,600 hits per second and crashed soon after it opened; in New York so many people panicked over any flu-like symptom that hospital emergency rooms were swamped with ten times more patients than normal, worsening care for those who really needed it.4

In China and other countries, border nurses quarantined anyone with a fever seeking to enter the country. Even though direct pig-to-human influenza transmission is exceedingly rare, Egypt ordered the slaughter of all the pigs in Cairo, impoverishing thousands of Christian small-scale farmers. And in Afghanistan, the nation’s only pig was quarantined.5

On June 11, 2009, Margaret Chan, the director-general of the WHO, announced that a “pandemic emergency”—or worldwide epidemic—of H1N1 influenza was officially underway. Governments around the world placed immediate orders for anti-flu drugs and vaccines worth hundreds of millions of dollars, as a new stock index, *RXFLU, tracked company profits. According to J.P. Morgan, up to $10 billion was spent globally on “influenza preparedness” in 2009, including over $4 billion by the US alone.6

The predicted dire emergency did not occur. In the 2009–2010 “influenza season” about 18,000 people died from the disease worldwide, fewer than in previous years, and the vast majority of victims had serious underlying conditions such as cancer, lung disease, AIDS,…