Probably no more than one in 10,000 patients might die, and the toll might be as low as one in 1 in 100,000 patients, said Nick Wilson, convener of the Pandemic Influenza Research Group, and a collaborator on the group, Michael Baker.
The two doctors at Otago University's Wellington medical school said a earlier estimate -- based on data from Mexico -- was for four patients in each 1000 to die, they said in a study published in the journal Eurosurveillance .
But they noted that if the novel swine flu virus, influenza A(H1N1), turned out to mainly affect the elderly -- who make up many of the victims of annual seasonal influenza -- the toll could be higher. Dr Baker said it was important for public health officials to know where to focus their battle against the pandemic: one possible reason for the relatively low proportion of fatalities in swine flu patients could be that it was mainly infecting young people.
The pandemic could last up to two years and see 30 percent of New Zealanders -- more than a million people -- infected.
The World Health Organisation has said the virus is spreading faster among people aged 10 to 45 years, and that its severity of the disease ranges from mild symptoms such as sore throat and muscle ache to severe illnesses including pneumonia.
So far, three people have been confirmed as having died of the disease in New Zealand, but Prof Baker said dividing reported infections by the number of deaths was not a true reflection of the fatality rate when infections became too numerous to be accurately counted.
At noon yesterday New Zealand had recorded a total of 1059 confirmed cases, but health officials said that the wide spread of the virus meant that only the most serious cases were being tested.
Of the 761 confirmed swine flu patients for whom ethnicity is known, 27.2 percent were Maori, 27.8 percent Pacific Islanders, 33.9 percent European, and 11 percent other ethnicities, Health Ministry figures show.
In the 2006 census just 14.6 percent of the population were Maori and 14.7 percent Polynesian.
Annual epidemics of seasonal flu kill about 400 people a year in New Zealand. Prof Baker and Dr Wilson presented four different methods for estimation the likely mortality rate of the swine flu, but noted all the methods had limitations and could be refined. Prime Minister John Key said yesterday that the Government had ordered a stockpile of a new swine flu vaccine for emergency workers as an insurance measure.
Mr Key said the Government had ordered 300,000 doses of a vaccine from Baxter Healthcare -- enough to give 150,000 the required two doses. It would be delivered within a month.
"Having the vaccine is primarily an insurance policy, we want to be in a position to have the vaccine rather than the other way around," Mr Key said.
Services included health, police, defence, border management, social support, corrections, fire, some aircrew and some foreign affairs personnel -- but targeted positions were staff who could be in direct contact with flu victims or virus samples.
Courses would be available for front line staff in Niue, Tokelau and the Cook Islands.
The vaccine is unlikely to be available until December because of the licensing process.
