This Year's Flu Vaccine Already Compromised.

ANDY JACKSON/FAIRFAX NZ

Roughly half of all flu-jabs administered to Kiwis during the 2015 winter season did nothing to protect them from illness.

Flu-jabs were less effective at keeping Kiwis healthy this year, with experts blaming a particularly tricky strain.

It comes after a nasty winter for flu sufferers, with hundreds hospitalised and several reported deaths.

Some experts say the effectiveness of flu-jabs against "flu-like illness" was potentially as low as 10 per cent in some parts of the country, given so many other winter viruses have been floating around.

However, doctors still urged everyone to get vaccinated, with any protection considered better than none.

Did you get the flu despite getting immunised? Contact news@dompost.co.nz

On average, flu vaccines usually work up to 60 per cent of the time.

Last year the dominant strain in this country was H1N1, labelled "swine flu", which mutated more slowly making it less likely to sneak past the vaccine.

But this year the H3N2 influenza strain proved dominant, and it was estimated that the flu vaccine were only effective about half the time.

Dr Tim Blackmore, an infection specialist at Wellington Hospital, said it was a rough year for winter illness, with vaccines appearing less effective, particularly among the elderly.

"There's been quite a lot of vaccine breakthrough this year."

Wellington saw a "much bigger than normal" number of hospital admissions for flu. An outbreak also raged through an older persons and rehabilitation unit in Hutt Valley for two weeks, infecting at least 13 patients and 20 staff.

In the community, several schools, early childhood centres and rest homes in the Wellington region were also hit by flu. In some schools as much as half the students were off sick.

But Blackmore said many of these winter illnesses were not the influenza virus, even though the symptoms were similar, meaning the effectiveness of vaccines against "flu-like illness" could be as low as 10 or 20 per cent.

However, even with those low figures, vaccines remained a safe and easy way to improve your chances of avoiding a potentially fatal illness, he said.

"You can argue over how well it works ... but I'd say have your jab and don't worry about it."

The flu season got off to a late start this year but a horror winter in the Northern Hemisphere, where H3N2 ripped through the population, led to a last minute rush to improve the vaccine for the Southern Hemisphere.

Virologist Dr Sue Huang from the Institute Of Environmental Science And Research (ESR) said vaccines for new strains take about six months to develop.

But in that time, H3N2 mutated into thousands of new variations, some of which changed so much they no longer responded to vaccine.

"We are chasing the virus' tail every year," she said. "Flu vaccines are not wonderful but they still keep a significant number of people out of hospital."

New Zealand had fared better than the Northern Hemisphere but the vaccine was still only partially effective.

"It's a little better, but could be better still," Huang said.

About 1.2 million Kiwis had a flu jab this winter. The season was far worse than last year and roughly similar to 2012.

The season peaked in mid August with infection rates dropping sharply since.

 - Stuff

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