On April 21st, the Centers for Disease Control and Prevention reported that two children in Southern California had developed a "febrile respiratory illness" caused by a flu virus that had never before been recognized in humans. The C.D.C. referred to the infection, in its Morbidity and Mortality Weekly Report, as a swine-flu virus, because some of its genes matched genes found in pigs. It was a deeply unfortunate—and largely misleading—choice of words.
It was misleading because most strains of the influenza virus consist of genes from pigs, humans, and birds that have combined in a variety of ways. Pigs, in particular, often serve as a mixing vessel for human and animal flu viruses, because the receptors on their respiratory cells are similar to ours. As it happens, this strain (formally known as 2009 H1N1) was new not only to humans; it had also never been seen in pigs.
The description was unfortunate because many Americans associate the term "swine flu" with one of the country's most prominent public-health debacles. In 1976, Army recruits at Fort Dix, New Jersey, became infected by a strain of influenza (another H1N1 variant) resembling the virus that caused the most lethal medical catastrophe of modern times, the Spanish-flu epidemic of 1918, which killed more than fifty million people. The Ford Administration, fearing the worst, attempted to vaccinate the entire nation. But the epidemic never arrived. A few of the millions who were vaccinated, however, suffered injury, and some even died. Trust in public-health officials was undermined, and it has never been fully restored. The episode helped establish a widespread fear of vaccines that—fuelled by groundless but impassioned claims about a link between autism and the measles vaccine—persists to this day. More than that, it created a false sense, shared by millions, that vaccines were at least as threatening as the diseases they prevent.
Fear spreads as rapidly as any virus, and in the weeks following the C.D.C. announcement the words "pandemic," "novel," and "swine" appeared daily in news accounts. In Mexico, where the epidemic gained its first foothold, two thousand people had been infected and nearly a hundred had died by the end of April. All schools, universities, museums, and theatres in Mexico City were closed. Sunday Masses, usually celebrated by millions, were cancelled. Experts noted that the influenza epidemic of 1918 had also been caused by a novel strain of the H1N1 virus. On June 11th, Margaret Chan, the director general of the World Health Organization, declared the highest level of international public-health alert, saying that the "world is now at the start of the 2009 influenza pandemic.'' She stressed that the new virus was spreading readily from one person to the next and from one country to another. The official tone of ominous foreboding had been established.
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