How Confusion Over COVID-19 Transmission Still Haunts Us


Two years after the pandemic began, we finally have a good understanding of how COVID-19 is transmitted: some infected people exhale virus in small, invisible particles (aerosols). These do not fall quickly to the ground, but move in the air like cigarette smoke. Other people can get infected when breathing in those aerosols, either in close proximity, in shared room air, or less frequently, at a distance. But the journey to accepting the overwhelming scientific evidence of how COVID-19 spread was far too slow and contentious. Even today, the updated guidance and policies of how to protect ourselves remain haphazardly applied, in part because of one word: “airborne.”

This fundamental misunderstanding of the virus disastrously shaped the response during the first few months of the pandemic and continues to this day. We still see it now in the surface cleaning protocols that many have kept in place even while walking around without masks. There is a key explanation for this early error. In hospitals, the word “airborne” is associated with a rigid set of protective methods, including the use of N95 respirators by workers and negative pressure rooms for patients. These are resource-intensive and legally required. There was a shortage of N95s at the beginning of the pandemic, so it would have been difficult, if not impossible, to fully implement “airborne” precautions in hospitals.

Due to its specific meaning in hospitals and longstanding misunderstanding about how airborne transmission actually happens and underappreciation of its importance, public health officials were wary of saying the word, even though it would have been the clearest way to communicate with the public about transmission and how to control it. As one article put it, “They say coronavirus isn’t airborne–but it’s definitely borne by air.” Because the word “airborne” was off-limits, it felt like we showed up to a basketball game thinking it was a boxing match.

During a press conference in February 2020, the Director-General of the World Health Organization said, “This is airborne, corona is airborne,” although a few minutes later, he corrected himself, “Sorry, I used the military word, airborne. It meant to spread via droplets or respiratory transmission. Please take it that way; not the military language.” In March, W.H.O. denied outright that Covid-19 was airborne, posting on social media, “FACT: #COVID19 is NOT airborne,” and calling it “misinformation.” We and our colleagues, scientists and engineers who have studied airborne particles for our entire careers, met with W.H.O. in April 2020 to express our concern that airborne transmission was important in the spread of COVID-19. W.H.O. vehemently rejected our suggestion and painted us as trespassers who did not understand what was happening in hospitals.

Likewise, the U.S. Centers for Disease Control studiously avoided using the word and instead tied itself in knots trying to describe transmission. Eventually we started to be heard, but the initial period of the pandemic, when stopping the virus was more feasible, and when everyone was paying sharp attention and was willing to adapt new protective behaviors, was lost. Protections that are nearly useless for this virus, such as surface disinfection and handwashing became deeply ingrained. Billions were spent on plexiglas barriers that may increase transmission. Gradually over the past two years, the two agencies have recognized transmission of the virus through the air, and in December 2021, W.H.O. finally used the word “airborne” on one webpage to explain how COVID-19 spreads between people, although the organization’s social media posts continue to completely avoid the word. The word remains verboten for C.D.C.

We are accustomed to talking freely about diseases that are waterborne, foodborne, bloodborne, or vector-borne. If even President Trump knew in February 2020, “You just breathe the air, and that’s how it’s passed,” why wasn’t the public told clearly the virus was airborne? According to conventional wisdom in the medical community, colds and flus were spread mainly by large droplets, and there was a very high bar to prove a disease was airborne. Historically, airborne transmission has been associated with long distances, beyond a range of 6 feet. Such occurrences are difficult to prove for a rapidly spreading virus, as our observations at that point were limited by rules restricting contact tracing to those within 6 feet due to long standing practice.

Read More: How to Clean Indoor Air Properly Against COVID-19

Ideas about how transmission works have been dominated by observations in hospitals, which tend to have excellent ventilation and therefore a lower risk of airborne transmission. Good ventilation removes the virus from the air and prevents it from accumulating over time, reducing the likelihood that someone will breathe in enough of it to become infected. As the pandemic evolved and we and our colleagues endeavored to show that all evidence pointed toward airborne transmission, public health leaders began to acknowledge that it could occur in special situations, namely those with poor ventilation. What they might not have realized is that, relative to hospitals, nearly all other buildings—homes, schools, restaurants, and many workplaces and gyms—would qualify as such special situations. In these buildings, indoor air might be replaced with outdoor air once or twice per hour, whereas in hospitals the ventilation rate is at least 6 air changes per hour in patient rooms and 15 in operating rooms.

We have studied viruses in the air long enough to understand that “airborne” is a trigger word in healthcare, yet we found it maddening that the word was off-limits during a pandemic. It was okay to talk about aerosols but not to say “airborne” or explain “like smoke,” even though it would have been far more effective for communicating with the public. To the general public, the word simply means something that is in the air, like a kite or pollen. The situation is like trying to explain a carcinoma diagnosis to a patient without using the word “cancer.” Using the word earlier in the pandemic would have facilitated the implementation of more effective mitigation strategies, such as Japan’s 3Cs—avoid close contact, avoid crowds, and avoid closed, poorly ventilated settings—instead of focusing so much on 6-foot distancing and surface cleaning. It also might have reduced resistance to masks.

The field of medicine should not have a monopoly on the word airborne. One way to reduce the chance for confusing communication in the future is to change the designation of different categories of precautions for infection prevention and control in hospitals. Rather than affixing specific words to the current categories—contact, droplet, and airborne—hospitals could assign numerical levels (e.g., 1, 2, 3, 4…) for different sets of precautions, such as those used for biosafety procedures in laboratories. This would avoid the association of certain words with regulatory requirements, freeing the words for general use.

From the outside, it is easy for us to see that a traditional, medical-centric approach has contributed to a sclerotic response to the airborne spread of Covid-19. We realize this sounds self-serving, but we need to recognize that broader expertise beyond medicine is required for public health, and certainly for combating an airborne virus. We, the two authors, know almost nothing about what happens to a virus when it’s inside your body nor how to treat it, but we do know how a virus behaves in the environment—whether indoors or outdoors—and how to remove it. This is the domain of environmental engineering, mechanical engineering, atmospheric science and aerosol science, fields devoted to understanding the movement and control of gases and particles in the environment. This type of expertise has been sidelined in our pandemic response.

We are thrilled to see the White House recognizing airborne transmission and the importance of indoor air quality through the Clean Air in Buildings Challenge as part of the National COVID-19 Preparedness Plan. While this is a good start, regulations and more funding will be needed to achieve clean air in all our buildings and fully realize its benefits in the long run. And because building operations are responsible for about 30% of greenhouse gas emissions, we must figure out how to do this efficiently.

We can’t let “airborne” be a dirty word. Instead, increased public attention to the air we breathe is an opportunity to dedicate science, technology, and policy tools to ensure that the air in our buildings is clean and healthy.

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