VERDICT
The 2-metre social distancing rule assumes that the dominant routes of transmission of SARS-CoV-2 are via respiratory large droplets falling on others or surfaces.
A one-size-fits-all 2-metre social distancing rule is not consistent with the underlying science of exhalations and indoor air. Such rules are based on an over-simplistic picture of viral transfer, which assume a clear dichotomy between large droplets and small airborne droplets emitted in isolation without accounting for the exhaled air. The reality involves a continuum of droplet sizes and an important role of the exhaled air that carries them.
Smaller airborne droplets laden with SARS-CoV-2 may spread up to 8 metres concentrated in exhaled air from infected individuals, even without background ventilation or airflow. Whilst there is limited direct evidence that live SARS-CoV-2 is significantly spread via this route, there is no direct evidence that it is not spread this way.
The risk of SARS-CoV-2 transmission falls as physical distance between people increases, so relaxing the distancing rules, particularly for indoor settings, might therefore risk an increase in infection rates. In some settings, even 2 metres may be too close.
Safe transmission mitigation measures depend on multiple factors related to both the individual and the environment, including viral load, duration of exposure, number of individuals, indoor versus outdoor settings, level of ventilation and whether face coverings are worn.
Social distancing should be adapted and used alongside other strategies to reduce transmission, such as air hygiene, involving in part maximizing and adapting ventilation to specific indoor spaces, effective hand washing, regular surface cleaning, face coverings where appropriate and prompt isolation of affected individuals.
…violent respiratory events’, e.g. coughing and sneezing, generate a warm, moist and turbulent gas cloud with forward momentum.
…Volume of speech may impact on droplet spread and subsequent risk of transmission,
…Clusters of coronavirus have occurred during prolonged ‘violent exhalation events’ such as singing or fitness dance classes in confined locations.
… Viral shedding (higher with coughing/sneezing) and factors related to airflow in indoor environments, such as ventilation, may increase droplet spread.
… odds of transmission in an enclosed environment were 18.7-fold higher than in an outdoor environment.
…environmental factors are important in addition to physical distance in determining risk of transmission.
… Factors suggested include virus concentration in respiratory fluid, levels of pollution or particulate matter in the air, humidity, temperature, indoor versus outdoor environments, symptomatic versus asymptomatic hosts, and an individual’s baseline susceptibility to infection.
…virus is also stable in air for at least 3 hours, with others suggesting it may be stable for up to 16 hours.
…Many studies were of retrospective design, and hence at risk of recall bias in terms of distance to infected individual and selection bias in terms of identifying recent contacts, particularly those that relied on contact tracing alone. Confounding variables, such as disease severity, time since symptom onset and contact with other individuals, were rarely reported.
Disclaimer: The article has not been peer-reviewed; it should not replace individual clinical judgement and the sources cited should be checked.
