Health experts have been surprised by a lower number of deaths throughout the country over the lockdown period.
During alert levels 3 and 4, public health experts found 548 fewer people died compared to the same period last year.
Otago University epidemiologists discovered the number of deaths dropped most noticeably near the end of level 4.
Otago University public health professor Nick Wilson told Morning Report seeing a reduction in respiratory diseases was surprising.
"Far fewer people were getting cough and fever symptoms. The lockdown did stop these viruses from circulating."
Niwa also found a significant reduction in air pollution which would have contributed to the lower overall death rate in respiratory diseases, he said.
"Air pollution is a cause of death in the elderly."
He said the data collated only showed the number of deaths, not the cause, which would become available at a later date.
"The road [death] toll goes down when unemployment goes up."
Wilson said many people with even the slightest respiratory symptoms stayed home and that was a practice that should continue.
He said New Zealand could adopt "the Asian practice of when people do have a respiratory illness they wear a mask if they have to leave the house".