National action on aerosol transmission of COVID-19

The following open letter is to the prime minister, federal health minister, state and territory premiers and health ministers, chief medical officers of the federal, state and territory governments and the members of the AHPPC, the CDNA and ICEG.

Australia must take urgent coordinated national action on aerosol transmission of COVID-19.
Urgent upgrades of respiratory protection for healthcare workers are needed as well as improved ventilation in healthcare settings, other indoor public spaces and private homes.

In July of 2020, 239 international scientists brought the issue of airborne transmission of SARS-CoV-2 to the world stage.[1]  Since the publication of their letter, there has been increased recognition of this route of transmission from the World Health Organization (WHO), Centers for Disease Control and Prevention (CDC), the European Centre for Disease Prevention and Control (ECDC), and other national disease control agencies.[2] [3] [4]  Despite overwhelming evidence to support airborne, or aerosol, transmission of SARS-CoV-2 [5]  [6]  [7]  [8]  [9] [10] [11]  this has not translated into appropriate and consistent public health and infection prevention control measures across Australian jurisdictions.  While other countries promote the “3 Cs” (avoiding closed spaces, crowded places and close-contact settings), Australian guidelines continue to stress droplet and contact transmission (guidelines from CDNA, ICEG, NSW CEC and others), which have led to a focus on measures of limited or insufficient effectiveness, such as deep-cleaning, handwashing, surface disinfection and 1.5-metre physical distancing.  It is imperative that people in all sectors understand the risk of airborne transmission, as well as the actions that can be taken to combat it.  To this end, specific strategies to reduce indoor aerosol transmission of COVID-19 are adeptly summarised in the Chief Science Advisor of Canada’s COVID-19 Expert Panel’s bioaerosol report,[12] the Occupational Safety and Health Administration (OSHA) Alert,[13] the Harvard TC Chan Risk Reduction Strategies for Reopening Schools Report,[14] the CDC’s “COVID-19 Ventilation in Buildings” guidance,[15] the European CDC’s “Heating, Ventilation and Air-Conditioning Systems in the Context of COVID-19: First Update”,[16] and the “ASHRAE Position Document on Infectious Aerosols”.[17]

The importance of airborne transmission has been highlighted by the German government, which has committed 500 million Euros to mitigating its effects in public buildings[18] “Lüften”, or airing, is now German policy and has been longstanding in South Korea, Vietnam, Taiwan and in other regions which embraced the principles of the 3 Cs early on in the pandemic. Indeed, China’s very first announcement of this novel coronavirus on 31st December 2019 also made public recommendations for ventilation of enclosed spaces, avoiding crowded indoor places and wearing masks.[19] The initial clinical guidance[20] on 24th January 2020 strongly recommended airborne PPE for clinicians. Italy, New Zealand and Japan have all accepted and now promote aerosol messaging.

With this evolving science, the importance of monitoring and improving ventilation has become increasingly clear and thus US, UK and Canadian government agencies have produced improved guidance.[21]  [22]  [23]  [24]  However, despite increasing global recognition and mitigation efforts,  there continues to be a lack of attention to the importance of ventilation in Australia.  The Australian Government has not produced any specific guidance  or mandated relevant standards.

This lack of acknowledgement of aerosol transmission has had far-reaching effects.  It has contributed to the healthcare outbreaks associated with over 3,500 healthcare worker infections in Victoria, healthcare facility closures across Melbourne and in Burnie, Tasmania. It seeded outbreaks into the community, resulting in further economic and social upheaval.  More recently, essential workers, such as paramedics and bus drivers transporting people in hotel quarantine, continue to use “droplet and contact precautions”, wearing poorly-fitted surgical masks, which unlike airborne protections (fit-tested N95/P2 respirators, etc.), do not afford any satisfactory level of protection against airborne pathogens in high-risk environments.[25]  This has led to infections in these workers and spread into the wider community, resulting in large outbreaks with major economic and social disruption.

To reflect the current scientific evidence, we call on the Australian authorities to:

  • Take the most urgent measures to reduce the risk of workers at the international border and in hotel quarantine becoming infected.  This must include the provision and wearing of airborne respiratory protection at all times for these workers, urgent vaccination with the highest efficacy vaccines, and urgent audits and upgrading of ventilation infrastructure.  Delays in these simple measures will increase the risk of further outbreaks in Australia and potentially allow the establishment of highly transmissible variants in the community which cannot be controlled as ‘easily’ as we have controlled outbreaks to date.
  • Update all COVID-19 guidance to emphasise the risk of aerosol transmission of COVID-19.
  • Mandate and fund ventilation assessments and upgrades of essential public institutions, such as hospitals, schools, aged care facilities and prisons.
  • Promote strategies to reduce transmission risk in private homes, businesses and other enclosed spaces through clear public health messaging and education. Avoid the “3 Cs” through indoor mask wearing when community transmission is present (even when physically distanced), routinely opening windows to refresh the air, regular HVAC maintenance and filter replacement or upgrade.
  • Ensure that no high-risk health care worker or other essential worker, including those in hotel quarantine, is denied access to a fit-tested respirator (N95, elastomeric or equivalent) for suspected or confirmed COVID-19 positive patients. 
  • Risk assessment for health care workers should go beyond the presence of “aerosol generating procedures” and should take into consideration aerosol-generating exposures (e.g., shouting, singing, coughing, sneezing, heavy breathing), proximity to the patient, time spent with the patient, indoor air quality, and patient compliance with mask-wearing for source control. 
  • Fast track research and recommendations into indoor air quality. This includes the study of carbon dioxide (CO2) monitoring as a surrogate measure of indoor air quality and airborne pathogen risk [26] with a putative threshold set at 600 PPM based on termination of a TB outbreak.[27]
  • Include recommendations on usage of air cleaners such as appropriately sized portable air filtration (HEPA) units or simple, practical and low-cost homemade devices using MERV-11/13 filters and box fans, as options for filtering out bioaerosols indoors when ventilation is suboptimal.
  • Engage engineers and other ventilation specialists to develop clear ventilation standards for indoor environments and integrate these standards into the reopening guidelines for businesses with a higher risk of aerosol transmission (e.g., restaurants, bars and gyms).
  • Convene a suitably diverse group of experts from aerosol science, engineering, HVAC, occupational hygiene, OH&S and organisational psychology to work alongside infection control experts, in accordance with the Australian Governance Principles.

Future respiratory viral pandemics are a certainty.[28]  Investing in ventilation, indoor air quality and appropriate personal protective equipment now will save lives and prevent economic hardship in the future.  The public health “sanitary reformers” of the late 1800s led the way in overcoming water-borne diseases like cholera and typhoid fever through investments in sewer systems and water treatment plants [29].  We are certain that there were those who thought the task at hand was insurmountable.  

We hope that Australia will consolidate the excellent work done so far in safeguarding our nation by rapidly translating the science on aerosols into action on the ground.  Addressing the fundamentals of disease transmission is critical to mitigating disease transmission.  Acknowledging and taking action on airborne transmission must be a key priority. It must be appropriately managed in all sectors to ensure an enduring recovery for Australia. 

Disclaimer: The views and opinions expressed in this letter are those of the individual signatories and do not necessarily reflect the official policy or position of any agency/institution.

Acknowledgements: With thanks to our Canadian colleagues, this letter is based on a Canadian letter sent on January 4th 2021[30]. A letter calling for similar measures in the UK was sent by a coalition of professionals on January 6th 2021.


[1]  Morawska L., Milton, D.K, “It Is Time to Address Airborne Transmission of Coronavirus Disease 2019 (COVID-19)”, Clinical Infectious Diseases, Volume 71, Issue 9, 1 November 2020, Pages 2311–2313,

[2] World Health Organisation, “Coronavirus disease (COVID-19): How is it transmitted?”, 20 October 2020,;

>[3]  ;

>[4] European Centre for Disease Prevention and Control, “Heating, ventilation and air-conditioning systems in the context of COVID-19”. 10 November 2020. Stockholm: ECDC; 2020, 

[5]  Fang, F.C., Benson, C.A., del Rio, C., Edwards, K.M., FowlerJr, V.G., Fredricks, D.N., Limaye, A.P, Murray, B.E., Naggie, S., Pappas, P.G., Patel, R., Paterson, D.L., Pegues,D.A., Petri Jr, W.A, Schooley, R.T. COVID-19—“Lessons Learned and Questions Remaining”, Clinical Infectious Diseases, ciaa1654,

[6]  Nissen, K., Krambrich, J., Akaberi, D. et al. “Long-distance airborne dispersal of SARS-CoV-2 in COVID-19 wards”. Sci Rep 10, 19589 (2020).

[7]  Kutter, J.S., de Meulder, D., Bestebroer, T.M, Lexmond, P., Mulders, A., Fouchier, R.A.M,, Herfst,S. “SARS-CoV and SARS-CoV-2 are transmitted through the air between ferrets over more than one meter distance”, bioRxiv 2020.10.19.345363; doi:

[8]  Lednicky, J.A.; Lauzardo, M.; Fan, Z. H.; Jutla, A.; Tilly, T. B.; Gangwar, M.; Usmani, M.; Shankar, S. N.; Mohamed, K.; Eiguren-Fernandez, A.; Stephenson, C. J.; Alam, M. M.; Elbadry, M. A.; Loeb, J. C.; Subramaniam, K.; Waltzek, T. B.; Cherabuddi, K.; Morris, J. G.; Wu, C., Viable SARS-CoV-2 in the air of a hospital room with COVID-19 patients”, International Journal of Infectious Diseases, ISSN: 1201-9712, Vol: 100, Page: 476-482, Publication Year 2020,

[9]  MacIntyre, C.R., Ananda-Rajah, M.R., “Scientific evidence supports aerosol transmission of SARS-COV-2” Antimicrobial Resistance & Infection Control 9, 202 (2020). 

[10]  Tang, J.W., Bahnfleth, W.P., Bluysenn, P.M., Tellier, R., Wargocki, P., Dancer, S.J.,  “Dismantling myths on the airborne transmission of severe acute respiratory syndrome coronavirus (SARS-CoV-2)”, The Journal of Hospital Infection,  12 January 2021,

[11] Samet, J.M., Prather, K.D., Benjamin, G., Lakdawala, S, Lowe, JM., Reingold, A., Volckens, J., Marr, L,  “Airborne Transmission of SARS-CoV-2: What We Know”, Clinical Infectious Diseases, ciab039,, 18 January 2021

[12]  Government of Canada, Office of the Chief Science Advisor, “The Role of Bioaerosols and Indoor Ventilation in COVID-19 Transmission”, 28 September 2020,

[13]  United States Department of Labour, Occupational Safety and Health Administration, “Covid-19 Guidance on Ventilation in the Workplace”, November 2020,

[14]  Jones E, Young A, Clevenger K, Salimifard P, Wu E, Lahaie Luna M, Lahvis M, Lang J, Bliss M, Azimi P, Cedeno-Laurent J, Wilson C, Segule MN, Keshavarz Z, Chin W, Dedesko S, Parikh S, Vallarino J, Allen J. “Healthy Schools: Risk Reduction Strategies for Reopening Schools”, Harvard T.H. Chan School of Public Health Healthy Buildings program, November 2020,

[15]  Centers for Disease Control and Prevention, USA, “Ventilation in Buildings”, updated 21 December 2020,

[16]  European Centre for Disease Prevention and Control, “Heating, ventilation and air-conditioning systems in the context of COVID-19”. 10 November 2020. Stockholm: ECDC; 2020, 

[17]  American Society of Heating, Refrigerating and Air-Conditioning Engineers, “ASHRAE Position Document on Infectious Aerosols”, 14 April 2020, 

[18]  BBC News, “Coronavirus: Germany improves ventilation to chase away Covid”, 19 October 2020,


[20] Huang, C., Wang, Y., Li, X., Ren, L., Zhao, J. & Hu, Y. et. al. (2020). Clinical features of patients infected with 2019 novel coronavirus in Wuhan, China. The Lancet. 395. 10.1016/S0140-6736 (20) 30183-5.

[21] Government of Canada, Office of the Chief Science Advisor, “The Role of Bioaerosols and Indoor Ventilation in COVID-19 Transmission”, 28 September 2020

[22] Health and Safety Executive, UK, “Ventilation and air conditioning during the coronavirus (COVID-19) pandemic”, 3 December 2020,

[23] SAGE-EMG, UK, “Role of Ventilation in Controlling SARS-CoV-2 Transmission” 

[24] Centers for Disease Control and Prevention, Covid 19, Community, Work & School, “Ventilation in Buildings”, updated 21 December 2020, 

[25] MacIntyre C.R, Ananda‐Rajah M.,Nicholls M. and Quigley, A.L. “Current COVID‐19 guidelines for respiratory protection of health care workers are inadequate” Med J Aust 2020; 213 (6): 251-252,

[26] Du, C‐RWang, S‐CYu, M‐C, et al., “Effect of ventilation improvement during a tuberculosis outbreak in underventilated university buildings”, Indoor Air202030422– 432

[27]  European Centre for Disease Prevention and Control, “Heating, ventilation and air-conditioning systems in the context of COVID-19”. 10 November 2020. Stockholm: ECDC; 2020, 

[28] World Health Organisation, “The best time to prevent the next pandemic is now: countries join voices for better emergency preparedness”, 1 October 20,

[29] Canadian Public Health Association, “Sewage and sanitary reformers vs. night filth and disease”,