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When a new virus is running rampant across the world, gaining a better understanding of its mechanisms of transmission is crucial for bolstering our prevention methods.
In a collaboration between The University of Hong Kong, Hunan Provincial Center for Disease Control and Prevention, and Sun Yat-sen University, researchers gained a greater understanding of the transmission method of the SARS-CoV-2 virus from a single pre-symptomatic case.
The subjects of the study come from a two-bus COVID-19 outbreak in China’s Hunan province. Using closed-circuit television images/clips and questionnaire surveys, the researchers were able to determine the participant’s seating position, boarding and alighting time, and whether they were wearing a mask.
The study revealed that the leading route of transmission for SARS-CoV-2 in a poorly ventilated indoor environment is through the air, and fomite transmission is negligible. The researchers highlighted a need for more targeted interventions in these poorly ventilated environments in order to stop the transmission of primarily airborne-spread viruses, SARS-CoV-2 included, and specifically found that a ventilation rate greater than 3.2 L/s per person is required for sufficient infection prevention.
These findings are a big discrepancy from the initial thoughts surrounding COVID-19, where the World Health Organization, in the pandemic’s initial phases, stated that SARS-CoV-2 could be transmitted through direct contact with a person or through droplets exhaled by an infected individual. Airborne transmission was initially considered unlikely, but in a 2020 update, the WHO recognized that airborne and fomite transmission may be possible.
Thanks to the Hunan province study, we now know that airborne transmission is the predominant transmission type, and fomite transmission has an insignificant impact in asymptomatic cases. Findings such as these can shape the methods of transmission reduction that we seek to implement in public settings, as well as guide our continual search to find the most efficient and effective methods of virus protection.
The impact of SARS-CoV-2 on our society is immense, with the virus’s rapid transmission highlighting areas of disease prevention in need of significant attention.
Perhaps one of the greatest challenges in halting a virus’s transmission lies in those who are asymptomatic—they feel perfectly healthy and so are unaware that they should distance themselves from others. Thus, those who are asymptomatic have a greater opportunity to spread the virus to those around them.
When infected individuals enter a poorly ventilated environment, they put those around them at risk, as evident in the Hunan province study, where just one pre-symptomatic individual initiated a COVID-19 outbreak. The implications of this emphasize the importance of proper ventilation since we cannot rely solely on complete adherence to self-imposed isolation, especially when taking into consideration asymptomatic individuals.
The truly groundbreaking nature of this study is that it utilizes data from day-to-day interactions, not situations overseen in a lab. The researchers were able to study transmission in real life, showcasing a need for additional studies of this same nature—those that observe viral transmission in everyday scenarios.
This study offers an unbiased look into how COVID-19 can spread from a single case to those around them, and we believe that this greater understanding of the virus’s mechanisms of transmission can be used to forge effective prevention initiatives—do you agree?
Share your thoughts on this unique study design and how we can better address the risk posed by asymptomatic individuals in the comments below. To further explore the Hunan province COVID-19 outbreak study, you can read the full article here.
Cheng, P., Luo, K., Xiao, S., Yang, H., Hang, J., Ou, C., Cowling, B. J., Yen, H. L., Hui, D. S., Hu, S., & Li, Y. (2022). Predominant airborne transmission and insignificant fomite transmission of SARS-CoV-2 in a two-bus COVID-19 outbreak originating from the same pre-symptomatic index case. Journal of hazardous materials, 425, 128051. https://doi.org/10.1016/j.jhazmat.2021.128051
