What we’ve learned so far about how Covid-19 spreads shows we need to re-evaluate how all respiratory infectious diseases pass among us, according to a new review in Science.
Up until the pandemic, it’s been understood that the small droplets we sneeze or cough – or what we picked up when we touched droplet-contaminated surfaces – were the main way respiratory viruses spread. Researchers write that droplets and surfaces alone can’t account for how the novel coronavirus is spread, and that airborne transmission – defined by the spread of aerosols – needs wider study for other viruses.
The SMC asked experts to comment on the research.
Leah Grout, Research Fellow, Department of Public Health, University of Otago, comments:
“This study highlights the role of airborne transmission of SARS-CoV-2 and the need to reevaluate aerosol transmission for other respiratory viruses. During the COVID-19 pandemic, the World Health Organization, the US Centers for Disease Control and Prevention, and others were slow to acknowledge airborne transmission of the virus, possibly in an effort to prevent public panic. This study recommends that protective measures including the ventilation and filtration of indoor environments, along with mask use and physical distancing, be used to reduce airborne transmission.
“To date, the issue of ventilation has not been adequately addressed in the New Zealand setting, and this will be an important consideration for controlling the COVID-19 pandemic and preventing future respiratory disease outbreaks. Some of the methods for improving ventilation are very easy, such as opening windows, and may have benefits beyond the prevention of disease transmission, with studies suggesting that improving indoor air quality may increase worker productivity and improve learning in schools.”
No conflict of interest
Dr Joel Rindelaub, Aerosol Chemist, University of Auckland, comments:
“This paper highlights how gaps in the knowledge of aerosol behaviour influenced early statements from health officials about the SARS-COV-2 pandemic, such as that the virus was not airborne.
“Aerosol scientists have long pushed for greater recognition of COVID-19’s aerosol transmission potential, with experts publicly questioning the WHO’s stance on airborne transmission since at least April 2020. After a letter signed by 239 aerosol scientists was released in July 2020, the WHO finally recognised that ‘short-range aerosol transmission… could not be ruled out’. It wasn’t until May 2021 that the CDC stated that aerosols were the main mode of transmission, 11 months after aerosol scientists had published the very same conclusion.
“Limited expertise on the generation and transport of respiratory aerosols may have an impact on infections beyond COVID-19, calling for a review on the health recommendations for other respiratory viruses, such as influenza virus, human rhinovirus, and respiratory syncytial virus (RSV).
“Thanks to the urgency driven by COVID-19, scientists have learned valuable information about the transmissibility of respiratory viruses, with no small credit going to the meticulous investigations of virus transmission here in New Zealand that have included events in airplanes and MIQ facilities.
“Since we know that the smallest aerosol particles, the ones that will travel the farthest, are enriched with the virus, the current recommendations regarding 1 or 2 metre distancing are not – and never were – sufficient to guarantee protection against COVID-19 transmission. This is especially relevant for indoor areas where ventilation and air flow are reduced compared to outdoor settings. The distance respiratory aerosol will travel is dependent on several factors, such as their size, the initial speed at which they are expelled, ambient air velocity, and other environmental factors. Thus, it may not be straightforward to recommend a universal distancing protocol. That being said, physical distancing of at least 2 meters along with focus on ventilation, airflows, air filtration, UV disinfection, and mask fit can be used to help prevent transmission of COVID-19.”
No conflict of interest