Those fears follow confirmation normal winter flu strains were no longer susceptible to the antiviral drug.
The number of confirmed cases of swine flu in New Zealand had risen to 303, up 45 from Sunday, with 219 active cases reported in the past seven days, the Ministry of Health said yesterday.
A 30-year-old woman remained in a critical condition in Wellington Hospital's intensive care yesterday, a hospital spokesman said.
Those diagnosed with the H1N1 strain had been prescribed Tamiflu.
But Environmental Science and Research virologist Sue Huang, head of the World Health Organisation national influenza centre in Upper Hutt, told The Dominion Post scientists feared swine flu could mutate with a Tamiflu-resistant strain.
All 18 seasonal influenza type A strains tested so far this year had been Tamiflu-resistant.
"Viruses are notoriously unpredictable . . . if there was mixing of the novel virus with other A(H1N1) strains circulating, such as in a person infected with both strains, the novel virus could take on resistant characteristics."
The ministry was now stockpiling another antiviral drug, Relenza.
Swine flu is also hitting the tourism sector.
Prime Minister John Key said yesterday the tourism industry was being hurt by swine flu as travellers in some countries put holidays on hold.
The number of visitors arriving in New Zealand from places such as Japan, Korea and China were down about 50% in the past month or so, he said.
"There is no getting away from the fact that swine flu risks damaging our tourism industry in the short term."
New Zealand was just one of more than 90 countries that had cases of the disease, so it was not in a unique position.
"It is just a fact that people become more hesitant to travel . . . you saw exactly the same affect when Sars happened, even though New Zealand did not have it."
People worried about many factors and not necessarily because they believed they were at greater risk in New Zealand, but it was too early to tell how much damage was being done, Mr Key said.
Nurses would stop asking international arrivals at Queenstown Airport to fill out location cards and no longer pursue contacts of confirmed cases, Public Health South medical officer of health Derek Bell told a swine flu seminar in the resort yesterday.
The team would move to the main airport area to supply information to tourists on where to go in Queenstown and what to do if they had severe flu-like symptoms.
If general practitioners became stretched, a flu clinic would be set up, but not at the hospital at Frankton.
Also speaking at the seminar yesterday, NZSki chief executive James Coddington said skifields had contingency plans for guests and 800 staff.
Children would be screened before being allowed into creches and all equipment sanitised.
District Mayor Clive Geddes said meetings had been held with retailers, schools, tourism operators and accommodation providers.
He was confident Queenstown would still be able to operate as a premier winter holiday destination once the illness arrived.
