Denial of Airborne Infection: A Review

'Air-Borne' by Carl Zimmer

Source: Published by Dutton

“Is no one interested in understanding the dynamics of airborne infection, probably the greatest single cause of morbidity in humans?”

The exasperation boils over midway through Carl Zimmer’s brilliant and compelling new book, Air-Borne: The Hidden History of the Life We Breathe. Though pitched in 1978 to the editors of the American Journal of Epidemiology, concerning their initial rejection of a landmark study of airborne measles in Rochester, NY, elementary schools, the question here has an oddly contemporary ring to it.

With fresh outbreaks of measles in 10 U.S. states joining influenza, whooping cough, and SARS-CoV-2 as confirmed airborne pathogens, five years into a pandemic in which that coronavirus has killed and injured millions worldwide, how is it still possible to bungle the mechanism by which these pathogens actually transmit? As Zimmer asks of the health agencies that published competing accounts of how SARS-CoV-2 spreads, despite knowing that individuals daily inhale two thousand gallons of air of varying quality and pathogenicity, “How could such a fundamental mystery about the worst public health disaster in a century go unsolved for so long?”

A Devastating Error

In answer to that question, Zimmer reminds us of a now-infamous tweet the World Health Organization sent out on March 28, 2020, barely four months into the global health crisis: “FACT: #COVID19 is NOT airborne. The #coronavirus is mainly transmitted through droplets generated when an infected person coughs, sneezes or speaks.” Following standard guidance on droplet infection, the agency recommended as preventive measures: “Keep 1 m distance from others; disinfect surfaces frequently; wash/rub your hands; [and] avoid touching your eyes, nose, and mouth.”

The next day, Zimmer recounts, the Los Angeles Times reported an outbreak of COVID among the Skagit Valley Chorale, a choir based in Washington state. The outbreak made international news because the group had carefully followed WHO and CDC guidance on droplet infection, including spacing themselves 1 meter apart, yet “COVID-19 [still] managed to slip into their midst.”

After several choir members fell gravely ill, those surviving agreed to participate in a study that determined from their position and path of infection that SARS-CoV-2, the virus causing COVID and Long COVID, was in fact airborne (Miller 2021). Disinfecting surfaces and even keeping 1 meter apart were, in turn, exposed as futile measures, in that they failed to prevent airborne infection.

Over the next several months, with vaccines fast-tracked but still far from approval, influential virologists and epidemiologists warned the WHO that its assertion that “#COVID19 is NOT airborne” was false and misleading, yet the tweet was neither deleted nor retracted. Indeed, when agency director Tedros Adhanom Ghebreysesus announced three years later, on May 5, 2023, that Covid-19 was no longer “a public health emergency of international concern,” even as 1,000 to 2,000 Americans were still dying weekly from the virus and its associated comorbidities, he let the mistake about non-airborne SARS-CoV-2 stand, allowing mistruths about its transmission and mitigation to spread almost as freely as the virus itself.

Driving Zimmer’s gripping account of these and related controversies, from 18th-century contagionists battling miasmatics to the Wuhan Institute of Virology’s gain-of-function research into lethal pathogens, obtuseness over airborne transmission recurs like an aggravating tic. That major world health agencies remain mired in 19th-century ways of thinking about infectious diseases is attributed to the intransigence of sanitarians like Charles Chapin and William Sedgwick, for whom airborne infection was broadly inconceivable and thus dismissed as of negligible concern.

When the Great Influenza pandemic struck Kansas in 1918, spreading from enlisted soldiers to civilians, it sickened hundreds every week, left more than 340,000 hospitalized over the next two years, and claimed more American casualties than World War I, World War II, the Korean War, and the Vietnam War combined. Yet despite the staggering numbers and manifest failure to combat spread, Chapin’s notion that “the air has no part in [influenza’s] extension from place to place” was routinely invoked as gospel, as an unchallengeable truth, even if to many specialists it was patently incorrect (Jimenez 2022; Mathur 2022).

Among health agencies today, incredibly, similar intransigence over droplet theory can still prevail, even as the guidance that accompanies it (“Keep at arm’s length from everybody and the chance of thus getting it is small”) was exposed at the time as hopelessly inadequate in failing to prevent mass infection, illness, and death.

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The Science of Airborne Life

Aerobiology—“the science of airborne life”—emerged in the 1930s, Zimmer shows, from the failure of droplet dogma. It drew from agricultural studies of fungal spores that routinely blighted wheat crops across the Great Plains, decimating their harvests. Emergent scholars in the field, such as William Firth Wells and his wife, Mildred Weeks Wells, argued that like windborne spores, aerosolized pathogens could “spread infection like smoke,” turning the air itself into a vehicle for transmission.

The Wellses succeeded in parsing differences in infection rates between humid and dry air, and in Mildred’s case, to show that UV light significantly reduced transmission in schools. Yet audiences hearing about their work were resistant and often unpersuaded. “They had accepted Chapin’s doctrines about the routes of infection,” Zimmer explains, “and couldn’t see a reason to give them up.”

Intolerable to Science or Revealing of Its Principles?

Considering the amount of death and morbidity that airborne pathogens like influenza, smallpox, polio, and SARS-CoV-2 have inflicted over the last century alone, it is galling to see the Wells’ innovative work on long-distance infection, community spread, and air filtration find a new generation of critics as intractable as Chapin and Sedgwick. Scant evidence was needed for their criticisms to stick—for large-scale experiments to be abandoned and for the thesis of airborne infection to be rejected wholesale, as if it were somehow hostile to science rather than revealing of its unseen, underrecognized principles.

When asked for his thoughts on airborne infection, the British influenza expert Christopher Andrewes is said to have “dismissed it very abruptly, [as] something to the effect that he did not think much of the droplet nucleus theory” of aerosol transmission.

For his part, even after the flimsiest of experiments on influenza, the Canadian microbiologist Ronald Hare decided to go further, rejecting the airborne transmission of all pathogens. He later would “attack” not just “the idea that [airborne] droplet nuclei could spread infection like smoke,” but its proponents as well. “It is extremely doubtful whether droplet nuclei play any important part in the transmission of respiratory infection,” he is quoted as opining. Then, modifying an immediate contradiction: “There is reason to believe that this may be a rare event.”

Aerosolized Hazards and Cold War Divisions

When Cold War divisions made aerobiology alluring to governments hoping to develop and stockpile chemical weapons and aerosolized agents such as anthrax to deter other countries from attack, public understanding of the risks and consequences advanced more rapidly.

Yet resistance to airborne mitigations—even modest, inexpensive, health-saving ones like the use of air filtration (HEPA) devices in hospitals and schools—remained intractable, even developing a history of their own.

During the Great Influenza epidemic, for example, when mask mandates were already in place in several U.S. cities, the American Public Health Association opted to hedge on whether to recommend masking beyond hospitals and barbershops. One of its commissioned reports concluded,

The evidence before the committee as to beneficial results consequent upon the enforced wearing of masks by the entire population at all times was contradictory.

Given the extreme and unrealistic framing here—“the enforced wearing of masks … by [all] ... at all times”—how could masks be proven conclusively to have prevented infections, even if rates of transmission fell after they were introduced? Their relationship had not been formally studied, leading the APHA to punt on recommending broader measures, even as 675,000 Americans would die from the airborne infection.

A New Study Reconfirms COVID Is Airborne

We now have a range of large, robust studies confirming that N95 and CaN99 respirators substantially reduce infection from airborne pathogens, with an assessed filtration efficiency of 97-98 percent without fit-testing. Surgical and cloth masks provide markedly less (though still not negligible) protection, with a filtration efficiency of 47-55 percent (Tomkins 2025). Are such studies heeded by authorities charged with providing guidance?

A landmark study in Open Forum on Infectious Diseases also reconfirmed last week that COVID is airborne, and the study of aerosol infection in Skagit Valley Chorale accurate in marking where WHO and CDC guidance failed (Roy 2025; Miller 2021). Using the same Airborne Infectious Research facility near Pretoria, South Africa, that years earlier had confirmed the airborne transmission of tuberculosis, with an exhaust pipe from infected ward patients making remote guinea pigs seroconvert, the study found evidence of far-afield airborne transmission of SARS-CoV-2 via infection from an unentered room, making contact or droplet infection impossible.

If we’re to learn from the failure of droplet measures for airborne pathogens, the Open Forum researchers and Zimmer’s Air-Borne underline, we could start by accepting that viruses and similar pathogens don’t limit how they infect people to pathways we prefer because they inconvenience us least.