A value of Reff > 1 means an outbreak is likely (the larger the value, the faster the increase in the number of infections). A sustained value of Reff < 1 means the virus will be eliminated from the community.

The alert levels correspond to interventions equivalent to (but not perfectly aligned with) New Zealand’s alert levels 1 to 4. The levels are: level 1 – prepare, level 2 – reduce, level 3 – restrict, and level 4 – eliminate.