New modelling shows strong interventions like New Zealand's alert levels 3 and 4 are successful at containing the spread of COVID-19, and our experience can help other countries.
The research, published by Te Pūnaha Matatini, was released on Wednesday afternoon. It measures Reff - a term for the average number of people that will be infected by a single contagious individual - and how interventions can reduce this to below an outbreak level.
"In response to the COVID-19 pandemic, a large number of countries worldwide have implemented or are planning to implement national-scale control interventions to slow or eliminate transmission of the virus," the report says.
"Our review of the extent to which interventions have successfully reduced Reff, a measure of transmissibility, informs future modelling to predict the outcomes we might expect from interventions employed in Aotearoa New Zealand."
First, the scientist gathered the number of COVID-19 cases in 25 different countries, states and provinces. They then compared each area's interventions, using New Zealand's level 1-4 framework.
By comparing the virus reproduction rates before and after interventions are in place, scientists are able to compare the impact of different levels.
The research found strong interventions have reduced the reproduction rate to below the level for an outbreak.
"In general, faster implementation and longer durations of sustained alert level 3-4 interventions yielded greatest reductions in Reff," the report notes.
"Greatest reductions are observed in locations with longer durations (more than 25 days) of sustained alert level 3-4 interventions."
This modelling helps authorities know what strength of intervention is required to achieve a desired outcome, and when interventions should be implemented or lifted.
Jacinda Ardern explains how New Zealand's alert system works
Alert level 1:
"In this phase we prepare - the basics like border measures, contact tracing and cancelling mass gatherings are all activated. You'll see that this is where we have been when COVID first arrived in New Zealand.
Alert level 2:
"Where the disease is contained, but the risks are growing because we have more cases. This is when we move to reduce our contact with one another, we increase our border measures and we cancel events. This is also the level where we ask people to work differently if they can, and cancel unnecessary travel."
Alert level 3:
"Alert level three is where the disease is increasingly difficult to contain. This is where we restrict our contact by stepping things up again. We close public venues and ask non-essential businesses to close."
Alert level 4:
"This is where we have sustained transmission. This is where we eliminate contact with each other altogether. We keep essential services going, but we ask everyone to stay at home until COVID-19 is back under control."