The impending arrival of a "life-threatening" Australian flu strain has Northland health officials worried about how hard the virus will hit the region.

Northlanders are being encouraged to get the flu vaccine as authorities await the arrival of a strain of the influenza virus from the northern hemisphere.

Northland DHB microbiologist Dr David Hammer said this year's flu season is likely to be "fairly severe" if the northern hemisphere experience is anything to go by.

He said the DHB is awaiting the arrival of influenza A (H3N2) - nicknamed the "Aussie flu" - from the northern hemisphere.

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The DHB has already seen a "small handful" of cases amongst foreign visitors in the past few months. They presented to the emergency department in Whangārei but were not admitted.

Authorities have updated this year's flu vaccine to include immunisation against the life-threatening flu strain A (H3N2).

The flu season in Australia last year was the worst since the 2009 "bird flu" pandemic, with more than twice the number of people admitted to hospital with influenza than is typical. The strain was linked to a rise in hospitalisation and deaths in the northern hemisphere.

ESR health physician Sarah Jefferies said countries such as Britain reported moderate to high levels of influenza and influenza-like illness during their 2017/2018 season.

She said the World Health Organisation recommended a change in the southern hemisphere vaccine for 2018 which better covers the strains of influenza detected in the 2017 southern hemisphere season and the northern hemisphere 2017/18 seasons.

Jeffries said there are four seasonal influenza viruses circulating globally and the vaccine covers all four strains. She said it is difficult to predict exactly what strains of seasonal virus will end up circulating in New Zealand's 2018 season. But the "life-threatening" Aussie flu had health officials worried.

"The health impacts of flu this year will depend on how well New Zealanders use preventative measures like immunisation and good hygiene practices, how the strains which circulate compare to viruses we've had previously, which cause natural immunity, and to the strains in the vaccine, which also generate immunity."

Jefferies said last year was a low-activity season in New Zealand, where influenza-like illness remained below the seasonal average. She said 2016 was also a very low-activity season.

"In view of the recently low-activity years, it would not be unreasonable to anticipate an increase in activity this year relative to the low seasons we've had recently."

Last year in the Northland DHB area the number of GP visits for flu-type symptoms peaked at 74 for every 100,000 in the week starting June 19. The national historical average seasonal rate for the same week is 48.4 per 100,000.

During the week beginning July 3 last year, there were 46 Healthline calls for influenza-like illness for every 100,000 people in the Northland DHB area.

Jefferies said the best option for prevention is immunisation, and the vaccine is free for older people, pregnant women and those with certain medical conditions.

So far 53 per cent of Northland DHB staff have been vaccinated. Acting chief executive Jeanette Wedding said the DHB is tracking well towards its target of 85 per cent.

"The higher the rates of vaccination for health professionals, the fewer people get infected," Wedding said.

About 400 New Zealanders die directly or indirectly each year from influenza, but figures are not available for Northland flu-related deaths.

Meanwhile, a stomach bug with flu-like symptoms appears to be hitting Whangārei hard. A post on the Northern Advocate Facebook page had several comments from parents whose children had been hit with the bug. Several people said it had passed from one member of the family to another.

ESR is launching an online dashboard which will provide up-to-date information on how the flu is tracking and its severity. The dashboard is aimed at health professionals but members of the public will be able to see it too.

It will include information on flu activity, flu severity, and which viruses are occurring this season.

Symptoms of the flu include:
-sudden onset of illness
-high fever
-headache
-a dry cough
-illness lasting 7-10 days

About one in four New Zealanders are infected with the flu each year. Many people won't feel sick at all but can still pass it on to others.
Flu viruses are mostly spread by droplets made when people with flu cough, sneeze or talk.

Other ways to protect yourself and your family:
-wash and dry your hands often
-stay away from people who are sick
-stay away from work, school or visiting people in hospital if you're unwell
-cover your coughs and sneezes