In early 2020, as word spread of a frightening new respiratory outbreak in China, the World Health Organization and the Centers for Disease Control and Prevention were pressed for advice. Both initially counseled social distancing, guided by the assumption that the disease was spread by large, boggy droplets that fell rapidly to the ground after being expelled by coughing or sneezing.
By avoiding such projectiles and keeping surfaces clean, the reasoning went, infection could be avoided. Yet this advice ignored—with tragic consequences—nearly a century of science suggesting that many respiratory diseases can spread via microdrops that are exhaled during normal breathing and can remain suspended in the air for hours.
In “Air-Borne,” the New York Times science writer Carl Zimmer seeks to explain how public-health officials could have overlooked such an important mechanism of the Covid-19 contagion. He begins his meticulous history with the ancient Greek physician Hippocrates, who taught that illness could be caused by “an invisible corruption of the air,” which he termed a “miasma.” By the late 19th century, studies by Louis Pasteur in France and Robert Koch in Germany established that disease was spread by germs, consigning miasmas to the dustbin of medical history.
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