New research from the University of Auckland suggests up to 80,000 New Zealanders could die from COVID-19 if strict measures such as the lockdown aren't in place.
The modelling was released on Thursday morning by Te Punaha Matatini, and shows lockdown measures can successfully suppress the spread for 400 days. But once these controls are lifted after 400 days, an outbreak occurs with a similar peak to an uncontrolled epidemic.
"Suppression can only delay an epidemic, not prevent it, but may buy enough time for a vaccine or treatment to become available," the study says.
"A combination of successful suppression, strong border measures, and widespread contact tracing and testing resulting in containment could allow periods when control measures can be relaxed, but only if we can reduce cases to a handful."
The modelling is based on 20 "seed cases", a transmission rate of 2.5 people and if there were no attempts to try and stop the spread of the disease.
It finds that 89 percent of the population would contract the virus within 400 days, leading to a 1.67 percent mortality rate or up to 80,000 people.
The study says that New Zealand hospitals could handle 40,000 cases, which is vastly less than the four million people they hypothesise could get infected.
A "mitigation strategy" is also suggested where the Government reduces the restriction level when the infection rate is low but raises it again when hospitals near their capacity. This would help develop herd immunity while not overwhelming the health system.
"In general mitigation requires an initial period of weak control to allow the epidemic to establish, then an extended period (3-4 months) of very strong control. This can be followed by periods when control measures can be loosened, but strong control needs to be re-established when cases increase towards hospital capacity," the study says.
But they say that amount of control over life hasn't been tested and only South Korea and China have managed to get their transmission rates below one.
"In those countries, this has been achieved by extremely intensive measures, including mandatory and strictly enforced quarantine, huge amounts of resources devoted to contact tracing, electronic surveillance of citizens' movements, etc."
The researchers say it's still unknown whether this low transmission rate is achievable in New Zealand since there's no evidence from "comparable, western democracies", including Italy who recently imposed a major lockdown.
It could also take up to two-and-a-half years for New Zealand to build up a herd immunity to COVID-19.