A recent post concluded that as churches move towards holding “worship services with limited congregations”, it would be necessary to consider the essentially “good practice” procedures adopted to date, in the light of more recent scientific information. On 26 May, the government published information on the scientific work which has been considered by the Scientific Advisory Group for Emergencies (SAGE). Here we reproduce extracts from these documents.
Environmental and Modelling Group of the Environment Agency [EMG] – Environmental Influence on Transmission
This 24-page report* was compiled by the Environmental and Modelling Group of the Environment Agency for the Scientific Advisory Group for Emergencies (SAGE), and is entitled Environmental Influence on Transmission of COVIS-19 – (28 April), (“the transmission report”). The Press Release is here.
The EMG considered four groups of questions around transmission focusing on:
- the relationship between time spent in an environment and risk
- the role of ventilation as a mitigating factor;
- the relationship between the 2m rule and transmission risk;
- the risk of transmission from contact with surfaces
These were considered in terms of published evidence, some early findings from simulations and some simple risk models. We have selected a number of extracts from the transmission report.
[Note: The 24-page version published on 26 May includes: Annex 1: Ranking workspaces by risk, Spatial and environmental typology , and a copy of the paper Environmental contamination and risk of infection for SARS-CoV-2, Marco-Felipe King et al. These have been omitted from the 15-page version, current at 28 May.]
Evidence of environmental dispersion for different mechanisms, and the risks and potential mitigations/measures of control within different environments from what we know about COVID-19: A brief evidence summary for SAGE, 14 Apr 2020
This is a 16-page report by SAGE, Evidence of environmental dispersion of COVID-19 for different mechanisms, (14 April 2020), (“the dispersion report”). The Press Release is here.
Key conclusions from this review are:
- The dispersion of virus is due to a complex interaction between people either generating or interacting with virus particles and conditions defined by the local environment. This includes the layout of the space and conditions including air movements and ventilation rates, temperature and humidity…
- Evidence from studies evaluating the physics of aerosol dispersion suggest that particles released from a cough or similar could travel much further than 2m, potentially up to 7-8m. Aerosol from environmental sources released in large quantities can travel further still under certain wind conditions…In many environments dilution by the airflow will mean that the risk of significant transfer of virus over large distances will be limited, however this risk has not been clearly quantified.
- There is limited conclusive evidence as to where transmission takes place, however one study from China indicates that it is very likely that the majority of transmission is in indoor environments.
- There is a challenge to relate physical models to actual infection risk, as the data on viral load released by people and remaining in the environment is very limited, and knowledge of infectious dose for different exposure routes is unknown.
- A key next step would be to identify specific scenarios of priority interest and convene an appropriate expert group to develop a strategy for modelling each one, to ensure models produce outputs that are relevant. This will most likely be engineers/mathematical modellers working with clinical, virology, public health and statistical experts, as well as the people who manage the particular environments of interest. Priority interest could be established by examining person density and frequency of visits for different environments, together with an initial assessment of local conditions (e.g. ventilation) to give a risk score that could be used to warrant deeper investigation.
We have selected a number of extracts from the dispersion report.
Information from the Government Office for Science, Coronavirus (COVID-19): scientific evidence supporting the UK government response, (“the overview”). This includes statements and the accompanying evidence “to demonstrate how the understanding of COVID-19 has continued to evolve as new data emerges, and how SAGE’s advice has quickly adapted to new findings that reflect a changing situation”.
The information in the transmission and dispersion reports is important in relation to the spread of COVID-19, whereas the overview documents provides an indication of the scope of the scientific work reviewed and that in progress.
Minutes of SAGE Meetings
On 29 May, government issued a Press Release on the release of the minutes from the Scientific Advisory Group for Emergencies (SAGE) meetings 1 to 34, up until the beginning of May. (200529). These minutes cover those from its first meeting to the meetings that took place at the beginning of May. “The minutes for meetings that have taken place after 7 May still contain sensitive information, with policy advice still under live consideration. These will be published in the coming weeks”.
There are a number of important caveats to bear in mind when reading these reports. All three sets of information, which were posted on 26 May, contained the statement [emphasis added]:
“The national and global response to the spread of COVID-19 continues to develop quickly and our knowledge of the virus is growing. These statements and accompanying evidence demonstrate how our understanding of COVID-19 has evolved as new data has emerged.
The evidence was often complied very rapidly during a fast-moving response and should be viewed in this context. The papers presented here are the best assessment of the evidence at the time of writing, and their conclusions were formed on this basis. As new evidence or data emerges, SAGE updates its advice accordingly. Therefore, some of the information in these papers may have been superseded at a later date.”
When citing such information, it is therefore important to identify the date on which it was presented and discussed. The overview report covered SAGE meetings over the period from 4 February 2020 (meeting 4) to 14 May (meeting 36); the paper on dispersion was discussed at meeting 25 on 14 April 2020; the paper on transmission was discussed at meeting 29 on 28 April 2020. Consequently, at the time of writing this post, the information had been considered by SAGE four to six weeks ago.
Another important caveat identified by the EMG (at ) was that “while data on other corona viruses can be used as a first estimate, there are not sufficient data on SARS-CoV-2 to confidently estimate infection risks at this time. Quantifying risk and contamination will require time to develop models and is specific to particular environments”.
What conclusions can be drawn?
Readers seeking clear guidance on when and how they might hold “worship services with limited congregations” will be disappointed. The two reports, presented 4-6 weeks ago, were based upon the state of knowledge at that time demonstrate, and confirm that:
- a substantial amount of work is in progress globally on the transmission and dispersion of coronavirus;
- much of this work is based upon mathematical models or laboratory-based experiments, not real-life situations;
- the mechanisms of spreading of coronavirus in real-life situations are highly complex and situation specific.
Nevertheless, there is broad agreement on many of the basic criteria:
- the use of the Risk = Hazard x Exposure methodology in assessing transmission risks;
- in the absence of hard science, risk assessment becomes important;
- the use of the “2 metre” rule was supported as general guidance for outdoor situations, but not as absolute guidance;
- the importance of personal hygiene, particularly hand washing, confirmed;
- the EMG considered it to be highly likely that short range droplet/aerosol and contact transmission dominate in most settings;
- whilst there is a degree of certainty in the role of droplets in transmission, the role of aerosols in uncertain;
- Occupant density indoors is a key factor in transmission, in relation to the likelihood of an infectious individual being present and the number of occupants who may be exposed. Building ventilation also a factor.
Consequently, there seems to be qualitative confirmation of the value of much of the current advice on precautionary measures but only limited quantitative information on their practical application.