The total number of deaths from swine flu in New Zealand last year is expected to exceed the 20 confirmed so far, deputy director of public health Dr Fran McGrath says.
A number of deaths were still being reviewed by the coroner, she said.
Deaths have been confirmed in 13 regions, including Otago.
Dr McGrath said accurate totals of the number of people who might have died from seasonal flu-like illness varied yearly.
In 2006, the total number of such deaths, including pneumonia, was 479.
It could be tempting to try to compare deaths and hospital admissions because of influenza in 2009 with other years, but it would take some years before such a comparison would be accurate enough to be useful, Dr McGrath said.
World Health Organisation information on the issue points out that the numbers of deaths because of seasonal influenza were estimates, and often testing was not done to establish that influenza was involved.
The models used for this data compared the number of deaths during epidemics of seasonal influenza with baseline data on deaths during the rest of the year.
During seasonal flu epidemics about 90% of deaths occurred in the frail elderly, who often had more than one chronic medical condition.
By comparison, the figures on swine flu deaths which were being released were based on laboratory-confirmed deaths, not estimates.
They would not give a true picture of mortality during the pandemic because testing might not have taken place, or deaths might be recorded as being because of an underlying medical condition.
