Vaccination rates have plateaued since September despite a third Omicron Covid wave that could cause record hospitalisations.
Figures from Te Whatu Ora/Health NZ show small batches of doses expiring throughout January, leading up to a batch of 592,000 that expires on January 31.
About 64,000 vaccinations are given out each month at the moment.
There is a chance the whole pile will not go to waste, as the Ministry of Health is asking Pfizer if it is possible to extend the expiry date of some batches.
Medsafe will review any evidence to support that.
Vaccinologist Helen Petousis-Harris said more was known about the longevity of the vaccine than when the dates were first set.
Covid cases are still rising, with this wave set to peak at the end of the month.
There has been little change to vaccination rates as a result, with just 46 percent of those over 50 having had their second booster.
Te Whatu Ora immunisation programme operations manager Rachel Mackay said vaccination rates were generally strong across Aotearoa but there was room for improvement especially in groups more vulnerable to the disease.
"In particular, we are striving for greater booster uptake among groups more susceptible to hospitalisation from Covid-19, including Māori, older people, and those with underlying health conditions," she said.
Petousis-Harris said there were likely several reasons for the stalled booster uptake, including a degree of vaccination fatigue.
But it could also be because so many people were getting the virus at the moment or had recently had the virus.
On December 14 the country had about 3.7 million doses stockpiled. Another batch of about 600,000 was set to expire on March 31 next year.
