Risk-informed decision-making for mass gatherings during COVID-19 global outbreak

Mass gatherings occur in a range of public places (e.g., spiritual and cultural settings, theatres, sports arenas, festivals, conference halls) and result in a large number of people being in close contact for extended periods of time.  Mass gatherings can contribute to the transmission of respiratory pathogens, such as the virus causing the current outbreaks of COVID-19. However, mass gatherings are not homogenous and the risk must be assessed on a case-by-case basis by Public Health Authorities, event organizers and relevant planners. Cancelling large events may be recommended from a public health perspective, but compliance and sustainability may be difficult and may cause significant social disruption and public resistance.

PHAC recommends conducting a risk assessment when determining the public health actions related to a mass gathering during the COVID-19 outbreak.  This involves assessing the epidemiology, related impacts, and the weight (importance) of each of the factors involved in the risk assessment.  The rationale for the potential health risks of mass gatherings include: increased crowd density, restricted points of access/exit which force participants through high touch areas (e.g. doors, elevators), and limited medical care. The diversity of spectators and participants can be varied which can increase the risk of communicable disease transmission due to close contact with people who have a diverse risk factors and/or immunological status. Limited environmental cleaning and the potential for individual health measures (e.g. hand hygiene) may play a role in increasing health risks at mass gatherings.

This tool was based on advice contained in the World Health Organization’s mass gathering guidanceFootnote 1.  Public Health Guidance on COVID-19 is available on Canada.ca/coronavirus, with community-based measures (including mass gatherings).

Decisions regarding mass gatherings can be considered on a continuum from no changes needed, to enhanced communication to attendees, to risk mitigation strategies being employed without cancelling the event, through to postponement or cancellation of the event.

Risk mitigation strategies could include:

Since mass gathering events, their settings, and participants/attendees are generally unique, the advice varies regarding which measures should be implemented.   Public health authorities and event organizers must work together to assess the situation. The following risk considerations related to the event, the disease and the environment/setting are provided to promote a systematic review of risk and to inform decision-making.  The classic epidemiologic triad contributes to the framework for risk assessment by highlighting the interplay between the host (in this case, the mass gathering event), the agent (SARS CoV 2 causing COVID-19) and the environment/setting (the broader context of the gathering in terms of its geographic location and associated resources).

Table 1. Risk considerations when deciding whether to postpone or cancel a mass gathering
Characteristics Risk considerations Implications Weight
Population attending the event Are persons attending the event coming from regions where there is community transmission of COVID-19 or from countries with unreliable surveillance of the disease? See affected areas list. If participants are expected from affected areas, the risk of importation is higher. These travellers may be self-monitoring for symptoms of COVID-19 for 14 days from their arrival in Canada, based on public health advice provided upon entry to Canada. High importance
Are persons attending the event members of a professional group that might have increased risk of infection? Healthcare workers may have greater risk of infection due to the possibility of occupational exposure. Medium importance
Are persons attending the event from demographic groups at greater risk of severe disease, such as older adults? Older adults, people with immune compromising conditions and chronic diseases appear to be at greater risk of severe disease, so consideration should be given to protecting them from possible exposure to COVID-19 cases.  Communication about risk to these attendees should be emphasized. High importance
Are persons attending the event at greater risk of spreading the disease, such as young children? Young children may be at greater risk of amplifying disease transmission so consideration should be given to protecting them from possible exposure to COVID-19 cases.  Reducing transmission among children indirectly protects the population and may therefore reduce the demand on the health care system.  Medium importance
Are persons attending the event members of critical infrastructure roles, such as healthcare workers? If transmission occurs at the mass gathering, participants may be subject to self-isolation or may become cases themselves. This could lead to critical infrastructure disruptions/absenteeism if the participants at the event represent critical services and industries. High importance
How many people are expected to attend the event? The larger the number of participants, the greater the likelihood of a participant being a case of COVID-19. Large numbers of people may also create greater likelihood of crowding. High importance
Event activities Will participants be participating in activities that promote transmission? Activities that could contribute to spread: singing, cheering, close physical contact such as when participating in contact sports, sharing food or beverages, etc. High importance
Crowding Is the event being held indoors, outdoors or both? Events held outdoors (i.e. higher ventilation) are likely to be lower risk than those held indoors. Medium importance
Will participants be consistently within 2 metres of one another? Respiratory droplets tend to fall within 2 metres of their source, so maintaining a 2 metre distance from others is a precaution to prevent spread.   Medium importance
Event duration How long will participants be gathered at the event? Longer events present more opportunities for transmission. Events at which attendees share overnight accommodation could also increase transmission risk. Medium importance
Event resources Will hand hygiene stations be available throughout the venue? Hand hygiene will be performed more frequently if alcohol-based hand rub or hand washing sinks with soap and disposable towels are readily available. Medium importance
Can event venue(s) be configured to maintain a 2 metre distance between participants? Respiratory droplets tend to fall within 2 metres of their source, so maintaining a 2 metre distance from others is a precaution to prevent spread.   Medium importance
Will there be health professionals or first responders at the event to screen and/or attend to someone who may be symptomatic? Although attendees with COVID-19 may not necessarily be identified through screening, this measure may identify some people with obvious symptoms which could help prevent spread.  Should someone become ill while attending the event, a health care professional should be familiar with appropriate PPE and IPC measures Low importance
Disease:  SARS-CoV-2 / COVID-19 (Refer to Summary of assumptions)
Transmissibility How readily does this disease transmit amongst people? Epidemiologic evidence suggests this virus transmits readily by respiratory droplets and contact. This suggests that attendance at a mass gathering could result in transmission if a case is present. High importance
Can people transmit this disease without symptoms? It is possible that cases transmit the virus in the early phase of their illness, when their symptoms are non-specific or mild. This suggests that attendance at a mass gathering could result in transmission if a case is present. High importance
Virulence How serious is the disease caused by this virus? Epidemiologic evidence suggests that COVID-19 manifests as a non-severe disease in most cases (~80 %), with a smaller proportion of cases developing severe pneumonia, and some dying.   High importance
Incubation period How long from the time someone is infected to the time they develop the disease? Estimated to be 5-6 days on average, with a maximum incubation period suggested to be 14 days. If people are infected at the mass gathering, they may not shown any sign of illness until after returning home, which could result in geographic dissemination of the disease. High importance
Evironment / Setting
Health system capacity Does the local health system have the capacity to assess, test and care for persons suspected of COVID-19, potentially in large numbers? Persons under investigation and cases of COVID-19 could present a substantial burden to the local health system if many require testing and care in a short period of time. High importance
Geographic location Is the location of the event geographically remote or in close proximity to a densely populated area? Geographic remoteness might limit access to tertiary care and may make it more difficult for a case to be repatriated. Proximity to a densely populated area could result in more rapid dissemination of disease. Medium importance
Local demographics  and epidemiology Is the local population at increased risk of severe disease if COVID-19 circulated? Some communities may want to reduce their risk of importation of COVID-19 due to characteristics of the local community, such as a high number of elderly residents, or higher rates of chronic disease. Medium importance
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