Image taken from the National Museum of Health & Medicine

In 2007, the Centers for Disease Control began assigning Pandemic Severity Index numbers to influenza epidemics, including pandemics from the past for which morbidity and mortality data is available. The scale runs from 1 to 5 and is based on the percentage of fatalities. The 20th century had three great influenza pandemics:

• The Spanish Flu of 1918-1919: Category 5, with greater than a 2% mortality rate. It killed between 20 and 100 million worldwide and 500,000 - 675,000 in the United States.
• The Asian Flu of 1957: Category 2, with a mortality rate of 0.1% - 0.5% of those infected. It killed between 1 and 2 million worldwide and about 70,000 in the United States.
• The Hong Kong Flu of 1968, also a Category 2. It left 1 to 4 million dead worldwide; 28,000 fatalities in the United States.

The Asian flu was first identified in February, 1957, in Guizhou, China. It made a rapid march across Asia and beyond:

• Mid-April: 250,000 people had been infected in Hong Kong.
• First week in May: 100,000 cases in Singapore.
• Mid-June: 2.5 million Japanese had fallen ill.
• End of June: virus had spread to India, Southeast Asia, and Australia.

United States military bases in Korea and Japan experienced outbreaks in April and May, and the first cases in the United States showed up in Naval and Coast Guard installations the first week in June.

The fact that the United States was prepared for the onslaught of influenza was largely thanks to a single individual: Dr. Maurice Hilleman, a scientist at the Walter Reed Medical Research Institute who was alarmed by news reports of the April outbreak in Hong Kong. Hilleman sent for specimens, and when they arrived the following month, he worked feverishly to determine whether Americans had any immunity to the strain. Deciding the population was vulnerable, Hilleman made a decision: “I put out a press release to tell the world that there was going to be a pandemic when school started in the fall.” In case the bureaucrats did not get the message, he alerted the World Health Organization, the CDC, and other government agencies as well.

President Dwight Eisenhower persuaded Congress to set aside $500,000 for vaccines, and 6 American companies worked triple shifts 7 days a week in an attempt to outrace the virus. The first vaccine became available in July. It was judged to be 45 - 60% effective, and 40 million doses were available by early November. Because the vaccines were grown in fertilized eggs, 200,000 roosters were allowed to live that autumn. Rather than going to the “frying pan,” the “patriotic roosters” became “national heroes,” one Washington Post reporter enthused.

Before the flu hit with a vengeance in mid-September, many speculated the threat was overblown. But early signs of a brewing pandemic within the US were there, for those like Dr. Hilleman who were paying close attention. In July, Louisiana schoolchildren who had been let out in the spring to help in the fields returned to their segregated schools; soon absenteeism in the white schools was 50%, and 10 of the 12 black schools had been forced to close. Also in July, 53,000 Boy Scouts attended the annual Jamboree in Valley Forge, Pennsylvania. Three hundred and fifty of them became ill at the camp site; the others returned home to seed the virus throughout the nation.

By mid-October, 29% of the schoolchildren in New York City were sick, and 16 schools had closed in greater Cincinnati, with 20,000 students and 200 teachers ill. In Fairfax County, Virginia, 33 schools were closed because of absenteeism, and the story was much the same across the country. The Centers for Disease Control estimated that 60% of America’s schoolchildren were sick with Asian flu during the fall. In October and November alone, 45 million people—25% of the American population—had been infected with the new virus.

The CDC estimates the death toll at approximately 70,000, meaning the odds an American died of the Asian flu during this time period were 1 in 2,457. Though the numbers are alarming, the fact that Americans were living in the age of antibiotics meant that pneumonia—the complication that had caused most of the deaths from the Spanish flu almost 40 years earlier—was treatable. The Surgeon General of the time, Dr. Leroy E. Burney, claimed the vaccine had saved millions of lives, but a recent assessment concluded that the vaccine was distributed too late in the natural course of the pandemic to have had any significant impact on the mortality rate.

Asian flu again made headlines in 2005, when 3,700 labs worldwide were shipped samples of the deadly virus. The virus sample was chosen because it was easy to grow and was classified as a Level 2 biohazard and therefore safe to use to test new vaccines and to train technicians to identify strains. Recognizing that no one born after 1958 had immunity, the CDC quickly recalled the samples. The last was found at the airport in Beirut, Lebanon, and destroyed. It has now been reclassified.