This year, according to data from the Institute of Environmental Science and Research, the Auckland metropolitan area has had the most hospitalisations from influenza-like illness since 2015.

While the data is only available for the Auckland metropolitan area, Te Whatu Ora national clinical director Dr Susan Jack says it's a good barometer of illness levels likely being experienced by hospitals across the country.

Maria Packe-Leonard, 53, died at Hutt Hospital on 21 July, and her husband, 53-year-old John Leonard, is still in a critical condition in Auckland's ICU after developing flu-like symptoms believed to be influenza A.

Te Arani Anthony Munro-Campbell, 27, died from influenza A while his mother lay in intensive care in Hawke's Bay Hospital in July.

And 16-year-old William Rollason died just days after developing flu-like symptoms - sore throat, runny nose and a cough - in June.

All were considered fit and healthy before contracting the virus.

What is influenza A?

Influenza, or the flu, is a viral infection. It can cause symptoms like a fever, chills, muscle or body aches, headache, runny or stuffy nose, cough, sore throat, upset stomach, vomiting or diarrhoea. Some people may have no symptoms, but can still pass it on to others.

Around one in four New Zealanders are infected with the influenza virus each year - most often between May and October.

Influenza A is one of four main types of influenza: A, B, C, and D. It is the most common type in New Zealand.

How long does it last?

It can take between one to four days to feel symptoms. Symptoms usually last about five days, but some can last up two to three weeks.

What is the contagious period?

Between one and two days before symptoms start until about day five.

What is the incubation period?

Usually between one and three days, but can be up to seven.

How do you test for influenza A?

Te Whatu Ora public health medicine specialist Dr Matt Reid says healthcare providers do not usually test for the flu.

"They usually diagnose you based on your symptoms," he says.

"They might order tests to make sure it is not a different illness if you have serious symptoms."

However, Dr Sue Huang, director of the World Health Organisation National Influenza Centre at the Institute of Environmental Science and Research, says a PCR (polymerase chain reaction) or a rapid antigen test can be used to diagnose Influenza A.

Can you die from influenza A?

Dr Reid says around 500 people die from the flu each year.

The flu virus changes often, with the H3N2 and H1N1 subtypes of influenza A the predominant strains in New Zealand, says Sue.

General Practice New Zealand chair Dr Bryan Betty says, anecdotally, more people appear to be affected "very, very badly" by these two strains compared to previous years.

"We know that every year some people can get very, very badly affected by the flu. And we've seen cases of that this year where younger people have been really, really affected by the flu and there have been a couple of tragic deaths across New Zealand."

People with an ongoing health condition - such as asthma, diabetes, cancer, a heart or lung condition, and other conditions that affect the nervous or immune systems, people with serious mental health or addiction issues, significantly overweight people, people aged 65 or over, Māori and Pacific people aged 55 or over, pēpi, tamariki, pregnant people and those who have just given birth have a higher risk of getting complications from the flu.

What are the treatments for influenza A?

Early use of antivirals, such as Tamiflu (oseltamivir), within the first 48 hours of developing symptoms, can reduce the duration of symptoms and the risk of complications from influenza, says Sue.

Otherwise, over-the-counter medicines such as paracetamol or ibuprofen may help to relieve fever, body aches and headache. Lozenges or gargles may ease symptoms such as a sore throat, runny nose and cough too.

Pseudoephedrine, an active ingredient in some medicines used to relieve nasal congestion, has been available at pharmacies without a prescription since May too.

How can you avoid getting influenza A?

The only protection against influenza is vaccination, sasy Brian.

This year, there are five quadrivalent influenza vaccines available in New Zealand: Influvac Tetra, Flucelvax Quad, Fluad Quad, FluQuadri, and Afluria Quad. They protect against two influenza A strains - H1N1 and H3N2 - as well as two influenza B strains.

The influenza vaccine is free for people aged 65 or over, people with a long-term medical condition such as diabetes, asthma, or a heart condition, children under four who have been hospitalised for respiratory illness, or have a history of significant respiratory illness and people with mental health conditions.

In 2022 and 2023, the influenza vaccine was also free for children under 12 and Māori and Pacific people aged between 55 and 64.

However, vaccine funding provided to Pharmac throughout the Covid-19 pandemic ran out this year.

Brian says this has likely led to a drop off in the number of people getting vaccinated.

It can cost up to $45 per vaccine, depending on how much clinics and pharmacies charge.

-RNZ.