Swine flu has become the dominant flu virus in New Zealand and some emergency departments are struggling to cope.
Hospital admissions for winter illnesses hit a high for the year last week, although numbers were well down compared to last year's outbreak.
Almost 1900 people visited hospitals in the week with flu-like symptoms.
One emergency department estimates up to two-thirds of patients have been given Tamiflu or its generic equivalent, oseltamivir.
Many Auckland schools reported about one child per class had been sick each day, and the city's hospitals said they were running near capacity.
In Northland, Whangarei emergency department clinical leader Scott Cameron said his team was overloaded: "It's very uncomfortable for us in terms of staffing and space."
Last year, many people with the flu were kept away from hospitals. But this year, people with flu-like symptoms have flooded emergency departments - and staff numbers are down with many having caught the flu themselves.
Swine flu - or, more accurately, Influenza A H1N1 09 - became a pandemic last year.
Waikato Hospital clinical microbiologist Chris Mansell said swine flu was currently the only influenza strain circulating New Zealand.
Dr Mansell's laboratory tests for patients in Waikato and the Bay of Plenty have found up to one in 10 patients with a winter illness had influenza, with only swine flu detected.
The Ministry of Health said tests showed swine flu was the predominant strain this year.
Swine flu is the year's biggest threat among winter illnesses, but it is already well established and therefore less likely to explode.
The Ministry of Health estimates more than a million New Zealanders - almost a third of the country - have been exposed to swine flu and have become immune to the strain, including those who received a vaccine.
People visiting hospitals with the flu were likely just a hundredth of the total with swine flu, Dr Mansell said.
People who are overweight or pregnant, smoke or have lung conditions could face complications.
Pregnant women with flu-like symptoms had a high chance of contracting a severe disease and were strongly urged to get immediate advice from their doctor, Dr Jarman said.
Dr Mansell said his Waikato laboratory was running at about 80 per cent capacity, and Ministry of Health figures show consultations are down as much as six-fold from last year.
But influenza usually spikes with a sudden upsurge spanning about two weeks, and this could still be coming.
Fifty-nine people were admitted to hospital with swine flu last week, bringing the total to 159. Two people have died from the virus this year.
Non-influenza viruses circulating New Zealand include rhinovirus and respiratory syncytial virus, which is highly contagious and demands isolation at hospitals.
* Almost 100 per cent of the country's influenza is now swine flu.
* Two in three patients with flu symptoms are given Tamiflu.
* One in three Kiwis have been exposed to swine flu.