health & science

Inside the flu’s spree of destruction

Each year influenza kills hundreds of New Zealanders, with three deaths already this season. In the fifth in a series on vaccine-preventable diseases, Farah Hancock looks at how you get the flu, what it does and why influenza viruses are a tricky moving target for vaccine makers.

It’s often your own fingers responsible for giving you the flu. 

If your fingers have touched something a sick person has sneezed or coughed on, chances are - inadvertently - your fingers will end up near your nose, eyes or mouth at some point before you wash them thoroughly.

Once the influenza virus has gained access to your body via your unwashed fingers, it goes on a Grand Theft Auto-like spree of destruction.

Starting in your respiratory tract, the virus carjacks cells, taking them over and then forcing them to replicate more virus cells. During this process your lungs become collateral damage.

Your immune system fights back, launching an attacking force of cytokines and chemokines. The chemokines also create huge numbers of T cells, an elite force of virus-seekers, and kill white blood cells. This increase in T cells causes inflammation like swollen lymph nodes. Mucous forms in your lungs and you begin to cough.

If you’re lucky, you’ll feel like you’ve been hit by a bus, spend an uncomfortable week in bed, and recover.

If you’re unlucky you might experience a complication, such as a secondary infection, or death.

Influenza can kill in a number of ways.

Sometimes, although not often, it’s friendly fire. The battle in your respiratory system between the virus and T cells can be waged too vigorously. If too much lung tissue is destroyed in the fight, the lungs become incapable of delivering oxygen to blood. This leads to suffocation.

More often, opportunistic bacteria will infect lungs weakened by influenza. Bacterial pneumonia is a common secondary infection. If you’ve been recovering from the flu and then get sick again rapidly, see a doctor immediately.

University of Otago’s professor Michael Baker said often there’s another way, which isn’t always recorded on death certificates. People with circulatory conditions can be affected.

“Because of the inflammatory effect of influenza infection, it precipitates heart attacks and strokes. Many of those people collapse and die suddenly outside of hospital, or perhaps in a rest or nursing home, or maybe in their own home.”

Respiratory illness can also be a post-influenza killer.

Baker said these groups add up to around 500 deaths per year in New Zealand, a figure higher than last year’s road toll. This makes influenza one of the biggest infectious disease killers in the country.

Most people who die are over the age of 65, however Baker said Māori and Pacific people were affected at a higher rate at younger ages.

“You don’t want anybody dying of influenza, but you don’t want people dying in that late middle-age period of 45 to 70. You shouldn’t be dying from influenza in those age groups, but that’s where we see really high rates in those Māori and Pacific people.”

Already this year it’s claimed the lives of a 12 year-old, a 20 year-old and a 62 year-old, and reported cases of influenza are sitting at a slightly higher rate than usual.

Current influenza rates are higher than usual for this time of year. Source: Ministry of Health

Across the ditch Australia had over 56,000 cases of influenza, with the April level at six times higher than any April on record. Already 139 people have died and it's predicted this could rise to 4000 by the time the flu season is over.

Worldwide, influenza is estimated to kill between three and five million people each year, with another 290,000 to 650,000 dying of respiratory illness related to influenza.

How to avoid influenza

The most effective way of avoiding the flu is not chopping your fingers off or putting a cone on your head to remind you not to touch your face, it’s vaccination.

Regular hand-washing is important, but a yearly flu shot is likely to be your best bet to avoid whatever viruses happen to be circulating.

Unlike other vaccines, which are needed once, with possibly a booster at a later date, the flu shot is needed every year, and unlike other vaccines, its effectiveness rate is lower.

This is because there are a number of influenza viruses and so far, a vaccine hasn’t been made which covers all the various strains.

Currently New Zealand has a publicly-funded vaccine which gives protection against the predicted four highest circulating strains for the season.The selection of the strains to immunise against is an annual decision made by a World Health Organisation panel. The four strains chosen are strains likely to effect the southern hemisphere.

There’s another reason too. Influenza viruses mutate, in a process called shift and drift.

Why you need a flu shot each year

Shift and drift sound like terms more likely to be used in car racing discussions than vaccine ones but the terms are related to why the contents of the vaccine changes regularly.

Influenza viruses are the disguise artists of the virus world. They change their appearance to escape any antibodies which might remember them.

This drift or shift can mean a person can get influenza more than once. What someone suffered from or was vaccinated against last year might not give them immunity to this year’s strain. What’s circulating this year may be a different virus, or it could be last year’s strain has drifted or shifted beyond what the body can recognise.

Small changes known as “drift” can occur in both influenza A and B viruses.

Imagine you are a shopkeeper with photos on your wall of repeat shoplifters you try to keep out of your store. If a shoplifter grew a moustache, he would still be easy to recognise and would be ejected. However, combine the moustache with a new hair colour, glasses and a hat, and there’s a chance the shoplifter will have drifted away enough from their usual appearance to get through.

“Shift” is a bigger, bolder change. It only occurs in influenza A virus.

Imagine the shopkeeper’s two worst repeat shoplifters had a child. This new shoplifter, with its parents’ tricks up its baggy sweatshirt sleeve, would be completely unrecognisable to the shopkeeper.

Shift is how viruses like swine flu evolved. The 2009 outbreak is estimated to have killed between 151,700 and 575,400 people.

The 1918 Spanish flu epidemic killed 8573 New Zealanders. This memorial plaque marks the burial site of over 1000 Aucklanders who died. Photo: russellstreet  CC BY-SA 2.0

Who can get the vaccine?

Almost everyone can get the vaccine.

“This is not a live vaccine. You can give it pretty well to anyone except somebody who has a very severe allergic reaction to any component of the vaccine,” said director of the Immunisation Advisory Centre Nikki Turner.

The catch is how well it will work. If you are undergoing chemotherapy, getting a flu shot won’t harm you, but your body might not develop antibodies. This is the same for infants which is why it’s important for pregnant or breastfeeding mothers to get vaccinated.

“If you give it to the mother in pregnancy, the mother will have an immune response to the vaccine. The mother will create antibodies. What crosses across the placenta are the mother's natural antibodies into the baby. When the baby is born, it has the mother's antibody protection against flu.”

The same immunity is shared through breast milk, although not as much as during pregnancy.

“They [flu vaccines] are not causing any dangers to the infants at all. We should strongly be recommending them.”

To date, 1.2 million doses of this season’s vaccine have been sold in New Zealand, a similar number to what was sold last year.

Vaccines are free for pregnant women, those over 65 years and under 65 with certain medical conditions.

For those who fall outside the free scheme, the shot is easily available for purchase from doctors. Since 2011, trained pharmacists have also been allowed to administer the vaccine.

Green Cross Health owns Unichem and Life Pharmacies. Spokesperson Debbie Yardley said the number of people opting to get a walk-in flu jab from their pharmacies has increased since the service was offered. In 2016, the pharmacies gave 18,000 vaccinations. Last year 60,000 were given.

She puts part of this down to more people knowing they don’t need to make a doctor’s appointment to get a flu shot as well as increased awareness that getting a flu shot is a way to stay well over winter.

Who opts out of the vaccine

Immunisation Advisory Centre’s Nikki Turner said one of the most common reasons she hears for not getting the vaccine is: “I had the flu vaccine, but I got the flu anyway.”

She said people seem to think the vaccine should always be 100 percent effective.

“Vaccine effectiveness overall comes out at around 50 percent. But we do know that [for] healthy children and healthy adults, it's more like 60 to over 60 percent effective.”

Another reason she hears is people saying they got sick right after getting vaccinated. She said this is not possible as it’s not a live vaccine.

“People might've been brewing a respiratory illness, were given the vaccine and got sick the next day and blame it on the vaccine. That's a coincidental effect.”

The final reason she hears is the “hero” response where people say they never get sick. However, she said this attitude generally changes once people have experienced a bad case of the flu.

Flu season usually peaks around the beginning of August and the vaccine takes around two weeks to work.

Read more:

Meningitis: a deadly alphabet soup

Measles: as certain as death and taxes

Polio: lingering effects and the last mile

Smallpox: a disease in deep freeze

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