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The SARS-CoV-2 Transmission Riddle - Part 13 (Revised January 2026)
The role of airborne transmission
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In our revised Riddle part 3, we concluded that the issue of transmission or respiratory viruses is much more complex than lobbyists and the media portray it to be.
We examined the evidence and provided our reasons for making this statement. The 1-to-1 model simply does not fit all the facts, and the transmission of respiratory viruses (if it occurs) remains understudied and poorly understood.
To our knowledge, no one has replicated our systematic search to understand precisely what is happening. This is a significant problem, as we need more independent research, free of politics, woke ideology, and lobbies.
The best example of these facts is the so-called airborne transmission.
The term airborne is confusing. In its current use, it encompasses a range of particles, from relatively large droplets to a fine aerosol mist. Large droplets (droplet nuclei) are generated during breathing or, more likely, coughing or shouting, whereas aerosols are generated by instrumental procedures in and out of hospitals.
Air, the simple air that we breathe, has also been indicated as a possible medium of transport of infectious particles. The possibility that air may be infectious has historically been a bone of contention for reasons that have more to do with social science and politics than with epidemiology.
Malaria, literally means bad air in Italian, and it was thought that malarial areas were such because of the presence of swamps which produce poisonous gases causing fever, so-called miasmata.
But malaria (like influenza) was a term used generally to indicate fevers rather than specific ailments.
The joker in the pack was the presence of breeding grounds for Anopheles mosquitoes, which was not fully understood until Sir Ronald Ross demonstrated the transmission of the malarial parasite, and we began to distinguish the presence of various agents and to identify their actions.
Centuries ago, the miasmatic theory came to be equated with opposition to germ theory or contagionism, thereby generating the polarised debate of contagionism vs anticontagionism.
To investigate whether SARS-CoV-2 can be transported by air from a contagious source to a person infected with the same strain (or, more accurately, lineage in the era of gene sequencing), we conducted a systematic review. This was initially funded by the WHO, a detail that, as we shall see, caused no end of problems.
Although 90 airborne studies we included in our initial review were conducted in healthcare settings, we immediately encountered recurring problems with the quality of the evidence, compounded by sampling issues. For example, 54 studies reported detecting viral RNA in air samples, but 69 different air samplers were used (some studies used multiple samplers), with substantial variation in sampling methods. This, coupled with weak reporting, made it difficult to distinguish between aerosol and droplet nuclei transmission routes.
The variability further limited interpretation of patient distance from the sampler, patient use of protective equipment or oxygen masks, time since symptom onset, patient activities (coughing and sneezing during sampling), air movement, air-conditioning sampler design, sampling method, storage and transfer conditions. Oh, dear.
The hospital environment is a suitable setting for this type of study, as the concentration of sick people should increase the likelihood of obtaining a positive sample.
Viral RNA was found in air samples, especially those from the ICU (as you would expect). It’s worth restating that the viral RNA detected by PCR is only a tiny fragment of the virus - PCR detects 20 base pairs from a virus that’s 29,000 base pairs in length. This minute fragment of RNA can attach to particulate matter and readily be found in the environment. However, detecting RNA in the air does not confirm transmission, as only infectious virions can cause disease; nevertheless, it can be a valuable tool for surveillance.
Of the 25 studies that attempted viral culture, 8 reported the growth of replication-competent viruses. A closer look at the methods and results indicates that some of the so-called positive cultures were due to other circulating viruses, not SARS-CoV-2, and that others had very low particle counts.
While the presence of SARS-CoV-2 genetic material in the air is not surprising, it was found at concentrations considerably lower than those of other agents, none of which are considered to transmit via the airborne route. In other words, the evidence for airborne infectiousness is weak.
The problem with the proponents of airborne transmission is that they see it as obvious, and, while ill-defined, they consider infectious virus particles to be everywhere.
This concept eventually sank miasma theory: it was everywhere, and for a time it could not be disproven, until a contagionist pointed out that deaths from infectious diseases (cholera in this case) were no different in London streets with tanneries than in streets with no miasmata and terrible smells. Contagionists were eventually also able to point to specific agents and specific routes of transmission, as in the case of anthrax, cholera and smallpox.
Credible airborne transmission studies are not easy to carry out. Interpretation is not straightforward, especially when the methods employed are so heterogeneous as to preclude comparison.
Proponents of the airborne route favour laboratory studies in which animals are subjected to unrealistically high concentrations of infectious viruses, and other variables, such as particle travel distance, are exaggerated. Particles generated by a human cough travel approximately 10 cm. A manikin expels particles at ten times that distance.
These experiments may be accepted as proof of concept. However, they cannot be applied to the real-world settings of crowded hospitals or large outdoor spaces, where conditions differ considerably.
Lobbyists censored our original review, and the journal editors struggled to find further peer reviewers for fear of intimidation. An example of misquotation of our review’s findings is the Corrigendum imposed by the editor on Rufino de Souza and colleagues after we complained.
At the time we concluded that the evidence was weak, but the airborne route of transmission could not be completely ruled out.
However, we didn’t stop there.
A further iteration and focussed version of the review is in print now (in pre-copy editing format)
The evidence is updated to 31 December 2024 and includes a smaller number of observational studies (26), 17 of which were conducted in hospitals, the likely most “productive” setting. We included studies comparing air samples with the likelihood of SARS-CoV-2 growth (viral cultures serving as the gold standard for infectivity and reproducibility, with concentrations still unclear).
There was considerable loss of data due to the usual heterogeneity in reporting, but the sampling distance from active cases ranged from half a metre to 14 metres. The review is open access; see the details. All you have to do is click on the link and download the pdf.
The conclusions are as follows:
“The proportion of positive SARS-CoV-2 viral cultures following positive RNA samples in the air is low, suggesting that while viral RNA may be present, the likelihood of detecting culturable, infectious viruses is substantially lower. Paucity of data prevents us from drawing conclusions about the threshold for viral infectiousness, as well as the relationship between distance and infectiousness. Discrepancies in the metrics used to determine viral load make comparison of research results across studies challenging. Therefore, the development of standardized guidelines for sampling and culturing viral particles from the air is warranted. To build a more robust evidence base, future studies investigating airborne transmission of viruses should consistently perform viral culture and genome sequencing to confirm infectivity and transmission chains.”
The conclusions are unlikely to be well-received by those with an agenda who are not scientists. Instead of promoting constructive discussion, agendas generate polarisation, especially in contexts of poor science. And the truth, as Pontius Pilate once remarked, slips through your hands.
This post was written by two old geezers who wash their hands.
Readings
Heneghan CJ, Spencer EA, Brassey J et al. SARS-CoV-2 and the role of airborne transmission: a systematic review [version 3; peer review: 1 approved with reservations, 2 not approved]. F1000Research 2022, 10:232 (https://doi.org/10.12688/f1000research.52091.3)
Onakpoya, I., Plüddemann, A., Rosca, E. et al. Viral cultures for assessing airborne infectiousness of SARS-CoV-2: a systematic review and meta-analysis. BMC Infect Dis(2025). https://doi.org/10.1186/s12879-025-12430-z
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