Mass gatherings are highly visible events with the potential for serious public health consequences if they are not planned and managed carefully. They can amplify the spread of infectious diseases and have the potential to cause additional strain on the health care system when held during outbreaks. The transmission of respiratory infections such as influenza has been frequently associated with mass gatherings. There have been examples of COVID-19 transmission during mass gatherings. Such infections can be transmitted during a mass gathering, during transit to and from the event, and in participants' home communities upon their return. Examples of mass gatherings include large meetings, conferences, sporting events, religious events, national and international events. It is recognized that while cancelling a mass gathering may reduce the viral transmission, it may also pose a barrier to personal freedoms. Mass gatherings may have cultural or religious implications (e.g. pilgrimages, large religious events) and cancelling such events may have significant cost considerations for jurisdictions, organizations and individuals. Decisions about whether to proceed with, restrict, cancel or postpone a mass-gathering event be based on thorough risk assessment undertaken by event organizers in consultation with all relevant PHAs (e.g., local, provincial, federal).

Considerations used in the risk assessment generally include: transmission dynamics, severity of illness, periods of communicability, incubation period, treatment options, potential for prevention (e.g., available vaccine, pharmaceuticals). Organizers should also consider the type of event (crowd density, nature of contact between participants, whether the event will be attended by registered on non-registered participants) and the host communities' capacity to respond to and mitigate the impacts of virus activity (e.g. health system capacity). A tool has been developed to assist planners with the risk assessment.

Measures to reduce the risks posed by mass gathering events include:

• Providing clear communication to participants before attending about the risks and advice on how to protect themselves and others to reduce virus transmission to inform individual decision making about attending the event
• Encouraging personal protective, individual and environmental measures by all attendees
• Increasing interpersonal distancing (ideally separation of at least 2 metres, not shaking hands, avoiding communal sleeping areas)
• Eliminating self-serve buffet style eating at social/religious gatherings
• Support frequent hand hygiene by providing hand sanitizers dispensers in prominent locations
• Discourage attendees from sharing food or drinks
• Requiring that ill be excluded people or those with high-risk medical conditions not to attend gatherings and ensuring event organizers have arrangements in place to safely isolate and transport people who become ill on-site remain the most important measures to prevent transmission.
• Implementing organizational measures for the event such as cancellation, postponement, or rearrangement of the event (e.g., offering virtual participation, live streaming to allow participation from a distance, moving venue from indoors to outdoors)