Alert color codes
For effective outbreak response, Green, Yellow, Orange and Red Zones can be continually identified and updated to help monitor the situation, to increase response effort where needed, and to release areas from constraints when possible. Individual Yellow, Orange and Red Zones should be as small as practical (neighborhoods, urban areas, counties/precincts, states).
Types of Zones
- Green Zones: Regions without confirmed cases or with a few infected travelers arriving from other regions
- Yellow Zones: Regions with a few cases of local transmission, but without clusters of community transmission
- Orange Zones: Regions adjacent to Red Zones or with small clusters
- Red Zones: Regions that have sustained community transmission
This color-coded zone-based scheme is based on the idea that in areas in which the virus is spreading within the community, the social connectivity must be lowered to the point where each individual infected will infect less than one other person on average. This decreased social connectivity will result in an exponential decrease in the number of new cases (although, due to the incubation period, there may be a time-delay before this is observed).
Travel restrictions/reduction allow for the more extreme social distancing measures (e.g. those in orange and red zones) to be implemented only in places currently experiencing significant local transmission rather than everywhere in the world at once.
For areas with only imported cases or a very small amount of local transmission (green and yellow zones), contact tracing may be sufficient to prevent the outbreak from growing, and thus the main goal is to avoid large social gatherings that allow for ‘super-spreader’ events. But if it becomes clear that the outbreak has not been contained to just a few cases (in which case it is very likely that there are additional unknown infected individuals), the number of new infections will continue to exponentially increase unless the measures for orange or red zones are immediately implemented.
The goal of both red and orange zone restrictions is to reduce general social connectivity to the point where there is an exponential decrease in the number of cases over time. In red zones, due to the higher numbers of cases (and therefore also the increased chances of exporting a case), stricter social distancing measures and travel restrictions are recommended.
For more information on medical and social responses, see:
Alert color codes
For effective outbreak response, Green, Yellow, Orange and Red Zones can be continually identified and updated to help monitor the situation, to increase response effort where needed, and to release areas from constraints when possible. Individual Yellow, Orange and Red Zones should be as small as practical (neighborhoods, urban areas, counties/precincts, states).
Types of Zones
- Green Zones: Regions without confirmed cases or with a few infected travelers arriving from other regions
- Yellow Zones: Regions with a few cases of local transmission, but without clusters of community transmission
- Orange Zones: Regions adjacent to Red Zones or with small clusters
- Red Zones: Regions that have sustained community transmission
This color-coded zone-based scheme is based on the idea that in areas in which the virus is spreading within the community, the social connectivity must be lowered to the point where each individual infected will infect less than one other person on average. This decreased social connectivity will result in an exponential decrease in the number of new cases (although, due to the incubation period, there may be a time-delay before this is observed).
Travel restrictions/reduction allow for the more extreme social distancing measures (e.g. those in orange and red zones) to be implemented only in places currently experiencing significant local transmission rather than everywhere in the world at once.
For areas with only imported cases or a very small amount of local transmission (green and yellow zones), contact tracing may be sufficient to prevent the outbreak from growing, and thus the main goal is to avoid large social gatherings that allow for ‘super-spreader’ events. But if it becomes clear that the outbreak has not been contained to just a few cases (in which case it is very likely that there are additional unknown infected individuals), the number of new infections will continue to exponentially increase unless the measures for orange or red zones are immediately implemented.
The goal of both red and orange zone restrictions is to reduce general social connectivity to the point where there is an exponential decrease in the number of cases over time. In red zones, due to the higher numbers of cases (and therefore also the increased chances of exporting a case), stricter social distancing measures and travel restrictions are recommended.
For more information on medical and social responses, see: