Rising power prices are compounding the problem as more people subject themselves to colder homes out of necessity, forcing many families into overcrowded living conditions that hasten the virus' spread.
Meanwhile, sick employees showing up for work are being asked to protect their colleagues this winter by staying home.
The Government spends about $18 million a year on vaccines to protect the at-risk population from influenza, with employers and individuals spending an additional $10 million on annual flu jabs.
The investment appears to be paying off, with Ministry of Health figures showing hospital costs for influenza-related admissions dropping from $7.3 million in 2010, to $1.5 million last financial year.
But despite the improvements, health experts caution against complacency.
Stay at home
Southern Cross Healthcare has issued a warning to Kiwis not to go to work sick.
According to a study of 97,000 staff last winter, almost half of Kiwi employers say staff are turning up to work sick when they should be at home.
Employees at small businesses were more likely to go to work ill than those at big organisations.
Despite the best of intentions, the stoicism of sick employees trying to soldier on actually exacerbates the problem.
The study showed an estimated 6.1 million days of work absences cost the New Zealand economy $1.3 billion during 2012 - a median cost of $837 per employee. Southern Cross Health Society chief executive Peter Tynan says limiting the spread of illness at work is crucial to cutting the country's absence bill.
"It's great to be committed to your job, and that should be celebrated, but the reality is that coming in when sick could actually cost your business a lot of money in lost productivity, disruption or temporary staff fees if others catch your bug."
Businesses can help limit the impact by encouraging staff to stay home, organising flu vaccinations, and providing tissues, hand sanitiser and wipes in the office, Mr Tynan says.
Don't underestimate flu
Virologist and National Influenza Specialist Group spokesman Lance Jennings says people underestimate the flu, often treating it as "just another bad cold".
But influenza is much more severe.
"The classical differences are the sudden onset, usually with a high fever, shivering ... a headache, and a characteristic dry cough which can go on for days and weeks after the initial infection."
Muscle aches are also common, and sufferers usually need bed rest to recover.
Flu is largely transmitted through droplets, which are propelled through the air when we cough, sneeze, or even talk, Dr Jennings says.
They usually drop within a metre radius, but it pays to be vigilant and keep your distance.
Adults unlucky enough to catch the flu will be contagious from 12 hours before developing symptoms, and remain infectious for up to five days.
Children can be contagious for up to 10 days.
"In our community, children are the great spreaders of respiratory viruses. [At school] you've got a large number of children together, they spend a lot of time indoors ... singing and talking. In winter the windows are closed so there's poorer ventilation and so this all enhances transmission."
When new flu strains are introduced, the impact can be particularly severe - and not just for the vulnerable.
The 2009 season saw 49 deaths from flu in New Zealand, a number of whom were young adults without underlying health conditions, he says.
In 2005, five young children died - three who had no existing health problems.
"Two of them didn't even make it to hospital."
The bulk of immunisation programmes are designed to protect more vulnerable sections of the population, like those with health conditions, pregnant women, and the elderly.
Strains of the vaccination are updated to match the viruses most likely to be circulating in the southern hemisphere during winter.
If the selection is identical to the virus circulating, vaccinations are effective in 90 per cent of healthy adults.
In cases when they're not identical, that figure drops to about 70 per cent efficiency.
Breathing room
Power companies, including Genesis and Meridian, recently announced significant increases in fixed electricity prices.
The changes will see many households pay 7 per cent to 8 per cent more for their power, with some facing increases of up to 24 per cent.
Toi Te Ora Bay of Plenty medical officer of health Phil Shoemack says rising power prices could assist in spreading flu.
"A family might be in a house which is appropriately sized for them, but during winter when it's cold and because of the higher cost of electricity they might choose to heat ... and live, in just one or two rooms in the house."
Influenza thrives in crowded situations like this, and one of the reasons it's so common in winter is because of our proximity to others.
"So there is a potential link between high power prices and an increased [flu] risk," he says.
The perception that venturing out into a blustery winter's day could catch you "the death of cold" is unfounded - flu is more likely to spread as a result of huddling together for warmth.
As for prevention, Dr Shoemack says vaccination is the only protection.
"There are lots of products that are touted by all sorts of people that will ward off your winter ills and chills. There's nothing to suggest that any of the various supplements and remedies have any positive benefit in stopping influenza."
Eating a well-balanced diet will give you all the vitamins and minerals you need, he says.
Who can be immunised?
Influenza immunisation is free until the end of July for pregnant women, people aged 65 and over, and anyone with long-term health conditions such as heart disease, stroke, diabetes, respiratory disease, kidney disease and most cancers.
Prevention tips
- Get immunised
- Cover your face when you cough or sneeze and wash your hands
- Keep your distance
- Don't go to work sick
- Eat a healthy and balanced diet