In April, 2020, as Covid-19 blazed like a wildfire, shutting down schools and filling hospital ICUs, President Trump held a White House press conference, flanked by eminent health officials, including Deborah Birx, tasked with the national response. In typical fashion, Trump rambled about potential remedies, from bleach to sunlight, even mentioning UV rays as a means of killing coronavirus. At the time reporters seemed to miss that, amid a mishmash of verbiage, the President was referencing an area of research long dismissed: germs often infect their hosts through airborne transmission and can be eliminated with UV. We now know that simple breaths can spark surges of illness, but until recently this theory was considered dead wrong. It took a pandemic to change the minds of experts.
In his virtuosic Air-Borne, Carl Zimmer, prolific author and a columnist for the New York Times, looks up, laying out the science of the air above and around us. A mere decade ago, most clinicians believed that pathogens infected only via fomites — surfaces such as furniture, kitchen appliances, or clothes — and coughs and sneezes within a radius of three feet. Germ-laden drops would fall to the ground. “Droplets” — less than five microns, or millionths of a meter — might linger in an unventilated room, yet they were benign. A maverick cadre of men and women thought otherwise: “In the 1930s, a few scientists challenged this consensus,” he notes in his prologue. “They argued that diseases could indeed spread on currents, that germs could float for hours like smoke. They recognized that airborne pathogens posed a fundamentally different threat than the one posed by short-range coughs and sneezes. They argued that some of the worst diseases known to humanity, such as tuberculosis and influenza, spread this way. Those scientists helped create a new field: the science of airborne life. They called it aerobiology.”
Zimmer’s narrative is rooted in the late Enlightenment, as scholars gradually rejected the notion of lethal illnesses associated with “miasmas,” foul gasses and odors clinging to impoverished ghettos. Biologists began experiments that would test hypotheses of infection. Among his many achievements, the 19th century French chemist Louis Pasteur proved that “spontaneous generation” couldn’t occur in a sterile environment. The English physician Charles Harrison Blackley discovered hay fever and, by extension, allergic reactions to pollen. (Charles Darwin wrote Blackley a fan letter.) These figures and their stories set the table for the 20th Century, when studies of the atmosphere transformed our grasp of pathogens.
The dawn of the American Century ushered in visionary investigations. The Spanish flu pandemic of 1918 had killed millions globally and an estimated 675,000 victims in the U.S., leaving psychic scars but also spurring innovations. Fred Meier took to the skies in crop dusters, leaning from the cockpit with Petri dishes to capture bacteria in the troposphere, and leading to the revelation that tiny forms of life teemed amid the stratosphere. Behind the scenes he collaborated with Charles Lindbergh and Amelia Earhart on their publicized flights. Decades later, Zimmer observes, “Scientists figured out how to read the DNA from microbes snatched from the air itself. In 2000, a team of scientists in Salt Lake City, Utah, pumped 70,000 gallons of air through a modern version of an aeroscope … They identified more than three hundred distinct genetic sequences, each possibly coming from a distinct bacteria. The air, it turned out, was a zoo.”
But the book’s stars are an eccentric married couple, William Firth Wells and Mildred Weeks Wells, whose intuitions about air transmission became a kind of Grail quest. Zimmer does right by this intriguing duo. Lacking proper academic credentials — William had analyzed oysters — the Wellses established a lab at Harvard and later at the University of Pennsylvania, after Harvard kicked them out. William Wells was a prickly perfectionist and long-winded bore; he alienated even ardent admirers. His volatile relationship with Mildred complicated their joint research. And yet his Infection Machine yielded insights that allowed his acolytes, the brothers Edward and Richard Riley, to challenge the status quo. Mildred’s UV tests, set in classrooms at Philadelphia’s elite Germantown Friends School, also pointed to airborne contagion. The Wellses never transcended the snobbery of their colleagues, though, and their work lapsed into obscurity after their deaths.
Zimmer seasons Air-Borne with vibrant characters, including the Wellses and the Jewish émigré Theodor Rosebury, a dentist-turned-scientist recruited during World War II to study the possibilities of biological weapons. This is the book’s most trenchant theme: science is shaped and driven by the political and cultural values of the individuals and institutions that fund investigations, whether private endowments or the federal government. (Consider Trump’s animus toward the NIH.) Zimmer’s layering of delectable anecdotes enhances his narrative. N95 masks, superior to flimsier surgical masks, were based on bra designs. Each spring a single white mulberry tree can release up to 486 billion pollen grains, dramatically boosting its odds of passing along its DNA, with breezes ferrying those grains to other white mulberries. Mother Nature, for instance, is always ahead of her large-brained primates, who struggle to understand her methods of selective advantage.
But what happens in the lab rarely stays in the lab: publishing and Hollywood have cashed in on our fascination with pathogens. In 1994, Random House brought out Richard Preston’s monster bestseller, The Hot Zone, which graphically rendered the debut of Ebola in western Arica. “The following year, a fictionalized form of Ebola became the star of the hit movie Outbreak,” Zimmer writes. “The movie follows a deadly virus as it spreads from Africa to California, mutating along its journey until it starts soaring from host to host — in one scene flying through the ventilation system of a movie theater and plunging into a victim’s mouth. ‘It’s gone airborne!’ Dustin Hoffman declares … There was no firm evidence that Ebola could spread among humans in droplet nuclei … When three lab workers later got infected with it, they experienced no symptoms at all. And in the full scope of global health, Ebola was not a major threat. By the 1990s, it had managed to kill only a few hundred people in total since its discovery. Meanwhile, tuberculosis — disease that Wells had clearly shown was airborne — was killing more than 2 million people every year but attracting woefully little attention. Poor people dying slowly of a preventable disease didn’t make for good ticket sales.”
As Air-Borne wends into the 21st Century — George W. Bush’s conflation of biomedical breakthroughs with the War on Terror; the 2003 SARS epidemic and a subsequent flare-up of MERS; Barack Obama’s handling of H1N1 — Zimmer’s gifts as a social critic step to the fore. He highlights inertia within the Center for Disease Control and World Health Organization, even as “Group 36,” a scrappy crew of researchers from Australia to China to Virginia, circled back to the Wellses’ abandoned data. The sclerosis among scientific institutions, the tip of the medical scales toward the rich and comfortable, gall Zimmer, but he weaves in damning details subtly, his tone dispassionate, far more effective than an incendiary polemic. He bookends his tale with the infamous March, 2020, Skagit Valley Chorale practice in Washington state, in which a contagious SARS CoV-2 singer infected 52 colleagues, an early superspreader event that steered Group 36 to the forgotten Wellses. Air-Borne, then, is heady reading and a sagacious look into the near-future, as other bird flus threaten to spill over.
Like fellow stellar science journalists, David Quammen and Ed Yong, teases out complex subjects with grace and clarity. Air-Borne soars while bringing to earth the web of invisible lives that connect to our own. “All told, from fires and dust storms, from crashing ocean waves and hurricanes, a trillion trillion bacteria cells are emitted into the air each year — a mass of more than 10,000 tons. Close to the same number of fungal spores are released as well, and with their bigger size, they weigh in at about 50 million tons,” Zimmer opines in a beautiful paragraph. “The aerobiome is a peculiar real: an ecosystem of visitors. A flea may hop into the air for a second, a diatom may be carried by the wind for days before falling back into an ocean, and a common swift can fly for ten months before landing to build a nest … While the aerobiome is transient, scientists now recognize it as a distinct zone of life, one that follows it own ecological rules and that exerts a powerful influence on the planet below.”
[Published by Dutton on February 25, 2025, 470 pages, $32.00 hardcover]