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University of Canterbury professor Michael Plank told Morning Report people's immunity from the virus after infection will likely weaken in the coming months.
Plank said given that there was an increase in infections during the months of February and March, as immunity wanes New Zealand could be hit with a second wave.
"Waning immunity means that over time people will become increasingly susceptible to getting reinfected and this could lead to a second wave sometime in winter or spring," he said.
Plank said the current increase in cases may be a result of easing of restrictions and people mixing socially.
He said the second wave was likely to be smaller than the number of cases in the first one.
However increase in hospitalisations and deaths depends on the age group that gets infected.
"If we start to see increasing numbers of infection in the older group in the second wave that could put the hospitalisation up to the sort of levels we saw in March and April," he said.
On Tuesday the country surpassed a million cases since the pandemic began more than two years ago.