From a Hashtag to the Right for Indoor Air Quality: A Short Story of the #covidisairborne Movement

Isolated during the first year of the Covid-19 pandemic, I started to follow on Twitter (the social media platform now called X) a few scientists who were dedicating part of their time to sharing information about disease prevention. From that personal curiosity emerged an interest in a feud happening between tweets, likes, and retweets: the World Health Organization had tweeted a “fact-checking” publication stating that Covid was not airborne. Denying the relevance of human-to-human airborne transmission of SARS-CoV-2 was seen as a mistake by some at that time, March 28, 2020, and came at a high cost for the organization’s public image.

Tweet from WHO on March 28, 2020 stating, “FACT: #COVID19 is NOT airborne.”

In this essay, based on part of my PhD dissertation research, I’ll elaborate how Twitter interactions played an important role in the scientific dispute around Covid transmission. Using the #covidisairborne hashtag as a hyperlinked clue (Leitão and Gomes, 2017), I navigated through different online and offline spaces such as social media platforms, podcasts, videos, live webinars, newsletters, webpages, and a chemical laboratory. When following those scientists on Twitter, their activity online involved interacting with similar-minded users and sharing their content, which started unveiling an international network of users with the same goal: to fight for the recognition of the airborne route as relevant to Covid transmission.

Every single preventive protocol for Covid was based on ideas of how transmission happens. Even unknowingly, they were always based on an interpretation of a “scientific fact.” If a public space had signs on the floor so people would keep a six-foot distance from each other, or if a school was implementing plastic barriers between students, they were targeting droplets coming from people’s mouths, heavy particles that follow a ballistic trajectory towards the ground. If N95 mask mandates were in place inside a hospital, the objective was to prevent airborne transmission. Aerosols are small systems that consist of particles (like viruses) inside of a material that can float in the air (like gases). They can float much further than six feet, even across continents, as sand from the Sahara desert can be found around the world. So every time a protocol for Covid prevention was adopted somewhere, it was based on a way of perceiving disease transmission.

However, aerosols in disease transmission are controversial. The most accepted hypothesis defended that bioaerosols are generated mechanically during “aerosol-generating procedures” (AGPs) such as intubation, thus airborne precautions should be in place only during those specific procedures in hospitals and clinical settings. During the SARS-CoV-1 emergency in 2003, different outcomes of SARS outbreaks in distinct cities were later attributed to the way transmission was understood and handled (Campbell, 2006): places where airborne precautions were taken had smaller transmission chains. The concept of the “precautionary principle” was invoked: when there’s uncertainty about the level of risk, the prevention strategies should be the most protective available.

The WHO’s official position in the first months of the SARS-CoV-2 pandemic focused on droplet transmission. It recommended cleaning hands and surfaces and social distancing as the main way to prevent getting sick, as can be seen in the “fact-check” tweet, which became a symbol of airborne transmission denial. To this day, although the WHO’s position on the topic has changed, the tweet has not been corrected or removed. Even though there wasn’t conclusive information on the virus transmission at the time, the tweet says Covid was not airborne as if it was an undeniable fact, without giving any space for discussion. As discussed by Latour and Woolgar, “a fact only becomes such when it loses all temporal qualifications and becomes incorporated into a large body of knowledge drawn upon by others” (1986, p. 106). However, the information being corrected was not only not completely incorrect, but it was actually derived from a WHO statement, where the possibility of airborne transmission during certain intrahospital procedures was considered and airborne precautions were recommended. So, although the WHO was telling the public that Covid was absolutely not airborne, it also said it could be situationally airborne (Greenhalgh et al, 2022), but many scientists disagreed on what those situations were.

What started with scientists replying to the tweet and discussing their official position on transmission rapidly turned into a movement that emerged with the “counter-hashtag” #covidisairborne, bringing together scientists and many citizens from around the world to discuss, plan advocacy strategies, and publish together. Despite differences, those in the movement largely shared the same logic, which translated into core values (such as the defense of the precautionary principle), beliefs (the certainty of the importance of airborne transmission), and objectives (the recognition of transmission and the end of the pandemic). That is, the movement proved a “thought collective” in the terms of the physician and philosopher of science Ludwick Fleck (1935[2010]). If we define “thought collective” as a community mutually exchanging ideas or maintaining intellectual interaction, we will find by implication that it also provides a special vehicle for the historical development of any field of thought, as well as for the given stock of knowledge and level of culture.

The Lack of “High-quality Evidence”

After the publication of the tweet in March 2020, thirty-six scientists got together on a Zoom videoconference organized by Lidia Morawska, a Polish-Australian physicist working on air quality. The scientists, joined by WHO representatives, sought to express their concerns on downplaying airborne transmission of SARS-CoV-2. The call didn’t go as expected, as the WHO position remained the same and the scientists were accused of “not having enough evidence” to back airborne transmission. In an article published three years later, those scientists disclosed what happened behind the scenes, even attaching the email exchanges following the first meeting, and argued that the WHO position was responsible for many of the lives lost by not following current evidence at the time nor the precautionary principle (Morawska et al, 2023).

In those emails and in many of the following statements, the WHO argued for the lack of evidence of significant spread of SARS-CoV-2 as airborne outside the context of AGPs. The word “evidence” was crucial: those who argued for droplet transmission as the main source of SARS-CoV-2 spread were usually infectious disease doctors and epidemiologists, who used the principles of evidence-based medicine to differentiate what would be “high-” and “low-quality evidence.”[1] On the “hierarchy of evidence pyramid,” systematic reviews and randomized clinical trials are at the top, while lab studies and case reports are close to the bottom. In the Evidence-Based Medicine (EBM) context, case studies are considered “anecdotical” and therefore shouldn’t be treated as evidence.

However, the #covidisairborne scientists didn’t consider randomized clinical trials as the gold standard for every scientific question. Instead, they understood different methodologies to provide more valid evidence on the topic of disease transmission, such as dedicated case analysis and mechanistic studies. They even rejected the conclusions drawn from randomized clinical trials, as those wouldn’t be able to really capture what was needed to understand disease transmission since scientists couldn’t purposely infect people with SARS-CoV-2. Thus if the “highest quality” methodology couldn’t design good studies in its own terms due to the nature of the scientific question, the meta-analysis came to the conclusion that there was no “high quality evidence” to support airborne transmission. For EBM scientists, this demonstrated a flaw in the airborne transmission hypothesis; for #covidisairborne scientists, it demonstrated a flaw in EBM.[2]

From that perspective, there was enough evidence at the time to consider Covid as airborne. Only a few of those thirty-six scientists were from the medical field; most of them were chemists, physicists, and fluid-dynamics specialists, so their perspective on good evidence was very distinct from the WHO representatives. It was not only a “battle” over disease transmission, but, in the end, a debate around the validity of evidence and what should be treated as such.

After going back and forth in communications, the “thirty-six group” wrote a public letter addressing the health community worldwide and got 239 scientists to sign it. The letter made it to the mainstream media around the world and turned the once-technical topic into a public issue. According to Douglas and Wildavsky (1983), the boundary between science and politics becomes blurred in the face of scientific dissent on risk. When the controversy is established, the issue becomes polarized and politicized, bringing scientists to the public arena as speakers and activists.

Even though there were no direct leaders in the #covidisairborne movement, the discussion orbited around key scientists who used the platform to disseminate information, call out public authorities, and organize strategies. These included Kimberly Prather, Jose Jimenez, Don Milton, Trisha Greenhalgh, and Linsey Marr. Many articles were published in prominent scientific journals addressing the main arguments and demands, which gave the public movement legitimacy, and the scientists also did hundreds of interviews and commentaries, leading the scientific narrative on traditional media.

However, the movement only strengthened because many non-scientists (such as myself) were interested in joining those discussions, amplifying them and contributing to the main objective. This approximation between scientists and citizens on a relevant and urgent issue contributed to the construction of a solid network of activists. It even resulted in non-specialists co-writing scientific papers in top journals alongside top scientists in the field, such as when they had made significant contributions like discovering historical aspects while researching the topic on their own. The hashtag became a symbol for a community, and was even used on social media profile descriptions to identify one’s position on the topic.

So, what could have been a technical discussion became a very passionate one: those who were involved saw it as a collective awakening to a scientific revolution and/or as a turning point for a paradigm shift, as chemists, engineers, and other fluid-dynamics specialists challenged the biomedical field on disease transmission. Many even traced the resistance to recognizing an airborne route to a resemblance of the miasma theory (Randall, 2021). The airborne denial was understood as the reason why the whole world was experiencing constant waves, new variants with higher transmissibility, and shocking numbers of deaths around the globe.

The WHO eventually recognized the relevance of airborne transmission in closed settings, but activists and researchers argue that the WHO’s changes were very subtle and silent, limited to a few pages on their website, with a gap in broadly communicating the new understanding of transmission. The introduction of recommendations regarding indoor ventilation, for example, was not necessarily related to an acknowledgment of widespread aerosol transmission of the virus but rather maintained the logic of poorly ventilated spaces as “specific” contexts where the virus could be transmitted. At the time of this essay’s publication, the organization has not launched any campaign revising its stance or using words as direct as those in the fact-check tweet, for example stating “Covid is airborne.” For those demanding this change, the WHO’s timid recognition was not enough.

Conclusions

Even though the Covid crisis is still officially an ongoing pandemic, with hundreds of thousands of new cases every day around the world and a solid number of deaths related to the virus, public attention to the topic has drastically fallen. As the “new normal” solidifies the post-pandemic experience of dealing with multiple Covid infections as if they are not harmful to vaccinated people, the #covidisairborne movement has also lost attention.

The #covidisairborne community, which also overlaps with the self-titled “Covid conscious community” on Twitter, has mainly shifted its efforts towards two main topics: Long Covid and air quality. Long Covid is a term for a range of symptoms and diseases related to post-acute sequelae of a SARS-CoV-2 infection, and many of the activists who advocate for adequate research and treatment are patients themselves. While trying to find relief for their condition, they advocate for the mitigation of transmission, particularly because there are almost no protocols in place around the world to contain the virus’s spread.

The topic of air quality was introduced early in the movement, as the collective mitigation of airborne transmission includes indoor air precautions, and also because many of the vocal scientists were air quality scientists. The 2024 Conference of the International Society of Indoor Air Quality and Climate was called “Sustaining the Indoor Air Revolution: Raise Your Impact,” and strategies for building on the “Covid momentum” were discussed throughout the meeting. Focusing on air quality was incorporated into the #covidisairborne movement as a way to demand solutions not only to the Covid crisis but to other respiratory diseases and future pandemics. With indoor air quality strategies, such as monitoring, ventilation, and filtration, there could be a significant reduction in respiratory disease transmission.

The case of the #covidisairborne movement serves to illustrate how Twitter posts and interactions have become a battleground for contemporary scientific disputes, especially during a pandemic. The platform served as a space for scientists, experts, and engaged citizens to challenge official narratives, share evidence and discussions, and organize various actions, including the construction of scientific knowledge in a traditional manner like publishing articles in journals. The controversy over SARS-CoV-2 transmission also exposed fractures and limitations in the perspective of Evidence-Based Medicine for certain scientific inquiries, particularly in public health crises where the time needed for producing scientific consensus is profoundly pressured by the need for interventions.

Notes

[1] The same argument was made to dismiss the need for masks, as I discuss in the third chapter of my dissertation. Some of the same WHO advisors published a Cochrane review on masks where, despite the known difficulty of assessing mask efficiency through randomized controlled trials, those were the only studies considered “high-quality evidence.” This led them to conclude that masks’ efficacy in preventing disease could not be confirmed and that there was no “evidence of benefit” in wearing them.

[2] The rejection of the “gold standard” of randomized studies was also used to defend the use of drugs like hydroxychloroquine and ivermectin in so-called early treatment strategies based on observational studies. Rosana Castro discusses this in an article published on Platypus in 2023: “Hippocrates Against Protocols: Experiments, Experience, and Evidence-Based Medicine in Brazil.”

This post was curated by Contributing Editor Clarissa Reche.

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