By David A. Shaywitz

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.

Though many experts at the time embraced the idea that disease could spread via contaminated droplets in coughs and sneezes, Mr. Zimmer notes, the notion that some pathogens could drift through the air faced skepticism. In the early 1910s, Charles Chapin, the health superintendent for Providence, R.I., sniffed that germs "have not wings" and enthused about the prospect of liberating medicine "from the specter of infected air."

But interest in airborne micro-organisms -- the "aerobiome" -- persisted. Fred Meier, a Harvard-trained botanist who began his career studying watermelon rot, became intrigued by the possibility that microscopic life floated all around us. In the early 1930s, he set out to gather samples from the sky, sending custom-made collection devices up in hot-air balloons and recruiting the pioneer aircraft pilots Charles Lindbergh and Amelia Earhart as collaborators. When Meier examined the haul in his lab, he discovered "an invisible zoo" of micro-organisms, including fungal spores and bacteria that had been suspended miles above.

The mysteries of air also attracted William Firth Wells, who arrived at Harvard in 1930 after studying water purification at MIT and helping rebuild the oyster population of Long Island Sound. Working with reclaimed laboratory equipment used to test poison gas in World War I, he studied the behavior of sprayed water and noticed a mist that lingered for hours, even days. Wells discerned that as relatively large droplets fell, they evaporated and became lighter. If small enough, the floating cores, which he termed "droplet nuclei," could be supported by faint currents of air.

Wells concluded that the clouds of breath we exhale can dissipate into droplets small enough to float through the air and be inhaled by others. He advanced the thesis with his wife, Mildred, whom Mr. Zimmer describes as "a strong-willed Texan woman who had endured a traumatic childhood and earned a medical degree in a class full of men." One experiment revealed that viable influenza viruses could be found in droplet nuclei 30 minutes after spraying a viral mist into the air, suggesting a potent mechanism for the spread of disease. A 1934 New York Times article expressed hope that the research would "shatter" the "comforting doctrine" that respiratory disease spread only by large droplets.

But as Mr. Zimmer points out, the doctrine didn't budge for nine decades. Meier died in a plane crash in the Pacific in 1938, and "his dreams for the science did not survive without him." William and Mildred Wells -- regarded as impressive researchers but "difficult people" -- fell out with colleagues at Harvard and soon found themselves looking for work. Worse still, public-health leaders continued to cling to Chapin's view of large-droplet spread.

While largely dismissed by the medical establishment, the idea of airborne contagion informed a clandestine bioweapons effort launched by President Franklin Roosevelt during World War II. Researchers at Camp Detrick in Maryland pursued a "deadly inversion of William Wells's research," Mr. Zimmer writes, seeking to increase the lethality of anthrax germs by dispersing them in a fine mist.

The next half-century of aerobiology research had a marginal influence. A 1996 set of CDC guidelines allowed that tuberculosis, measles and chickenpox could be transmitted by air and required special precautions in hospitals. Yet the guidelines exempted influenza and mumps, since these diseases supposedly spread in larger drops. A pandemic-preparedness plan issued by the Bush administration in 2005 acknowledged how little was known about the way influenza spread, as did a CDC workshop convened five years later, after a severe influenza outbreak. However, public-health agencies continued to assume that influenza was mostly spread by large drops at close range and could be avoided by maintaining a modest distance from infected people, even though, as Mr. Zimmer writes, "there was little firm evidence that any of this was true."

While the field of aerobiology may have entered the new millennium stuck on a "stagnant plateau," as one journal article lamented, hope was starting to emerge. Advances in technology led to a more complete characterization of the aerobiome. A range of scientists from around the world, meanwhile, re-examined the possibility of airborne transmission and discovered the evidence against it wanting.

Following the emergence of Covid-19, many of these researchers were appalled by the seemingly reflexive -- "mind-boggling," in the words of one scientist -- rejection of airborne transmission by public-health agencies. At first, these renegades individually struggled to have their work published but were largely rebuffed.

After an early Covid-19 outbreak among a choir in Washington state was initially attributed to large-droplet spread, a more detailed analysis by a unified group of skeptical researchers suggested that airborne transmission was far more likely. On Dec. 23, 2021 -- nearly 21 months after tweeting "FACT: #COVID19 is NOT airborne" -- the WHO "finally issued a clear public statement that the virus was airborne," Mr. Zimmer writes. A triumph for persistent scientists, perhaps, but also a pointed reminder of the complexity, fragility and deeply human dependencies of evolving science.

--Dr. Shaywitz, a physician-scientist, is the founder of Astounding HealthTech, a lecturer at Harvard Medical School and an adjunct fellow at the American Enterprise Institute.

(END) Dow Jones Newswires

March 14, 2025 11:48 ET (15:48 GMT)

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