This year's flu season appears to be tapering off after an early start – but officials aren't counting out a spring encore.

Crown agency ESR also couldn't say whether the unseasonably mild start to winter had any impact on flu spreading this year.

The latest surveillance showed a continuing drop in numbers of flu and flu-like illnesses (ILI) around the country for the fourth week running.

Nationally, there had been about 850 GP consultations, compared with a peak of more than 2600 at the beginning of July.

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Over the same period, the number of people testing positive for a flu virus has dropped from close to 1800 to over 500.

Rates of hospitalisation for severe respiratory illness, monitored by ESR in the Auckland region, have also dropped below the baseline seasonal level.

ESR public health physician Sarah Jefferies said this year's influenza season was early and appeared to be declining earlier than usual.

"When comparing New Zealand's current community ILI rates with the past few years, we are at similar levels to those seen in 2017, but higher than rates seen at this time of year for 2016 and 2018, which were particularly low years for influenza activity," she told the Herald.

"Although, community influenza activity remains below the seasonal baseline level at low rates, influenza viruses are still circulating in the community, with a higher than usual proportion of influenza-like illness being due to an influenza virus - as opposed to a common cold virus, for example."

It was unclear whether the climate – the first half of the year had been among the warmest on record – had played any part.

"Many factors affect year-by-year influenza rates, such as how well New Zealanders use preventative measures like immunisation and good hygiene practices, and how the strains which circulate compare to viruses we've had previously, and to the strains in the seasonal influenza vaccine [which also generate immunity]," she said.

"This year, so far there has been a good match between the circulating influenza viruses and the strains included in the seasonal vaccine."

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The flu pattern in New Zealand had also been similar to Australia's in some ways.
Australia saw an early start to the season, and a decline in numbers over the past month.

They have also had flu A and B viruses circulating, although, with a higher proportion of A viruses circulating than in New Zealand.

Each of those strains had tended to affect population groups differently.

"For example, influenza A viruses often cause more illness in elderly populations and influenza B viruses often affect younger and school aged children relatively more," she said.

"It also tends to be true that the elderly are over-represented in the hospital wards with influenza, whilst school aged children with influenza are over-represented among GP consultations."

While the figures indicated an early end to the flu season, Jefferies cautioned it was still possible there might be more to come.

"ESR will continue influenza surveillance until September as it is possible that there may be a resurgence in influenza cases later in the season."