More people than previously thought are being hospitalised because of infections caused by the flu.
It is one of the first findings of an international flu study carried out in New Zealand over the past winter.
Researchers at Crown research institute ESR say the rate of hospitalisations from flu this winter was the fourth highest recorded over the past 12 years.
The Shivers study focused on Auckland, where researchers say 1370 cases of severe acute respiratory infections were recorded between April and September - 23% of them caused by flu viruses.
Infants under one had the highest hospitalisation rate, followed by those over 80.
There were 38 admissions to intensive care and seven deaths.
Nikki Turner, head of the Immunisation Advisory Centre at Auckland University, says children who are at risk of flu should be vaccinated from the age of six months.