Influenza is ripping through Wellington schools and rest homes, with one flu-struck family likening the illness to an exorcism.

Regional Public Health has sent out a warning to all schools, early childhood centres and rest homes in the region after nine separate outbreaks.

It comes as New Zealand is gripped by the worst flu season since 2012. On Sunday, Christchurch woman Correna Healey, died a week after contracting the flu and later developing pneumonia.

Figures released on Thursday show reported flu-like illness continuing to rise with 345 in the past week, up from 319 . The South Canterbury and Tairawhiti, centred around Gisborne, areas have had the highest reported rates.

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Wellington lawyer Michelle Lander, her partner James Bell, and two sons Rafael and Hunter, have been knocked out for weeks after Rafael brought the sickness home from daycare in late July. Lander was driving her son home when he projectile-vomited into the back of the front passenger seat.

"It was like an exorcism ripping through the car," she said.

Within 24 hours he whole family was ill, all of them vomiting dozens of times throughout the night.

"I thought, 'What the hell is this? Have we got Ebola?' "

The family couldn't eat much for a week and Lander said she had only come right in the past few days. Her doctor, when she managed to see him, said the family had probably all had the influenza B strain.

Medical officer of health Annette Nesdale said some schools in the Wellington region had as many as one in five students off sick, and swabs had confirmed flu was the likely culprit.

Outbreaks had occurred in at least four schools, four rest homes and one early childhood centre.

"In the last 10 days, especially, flu has been increasing and we expect we will see more schools and long-term care facilities with outbreaks in the next week or two," she said.

With an increasing prevalence of flu, the risk of the rarer but more dangerous meningococcal disease had also increased, she said. So far there had been two cases in the region this year, including one in July, but this was expected to increase.

Ministry of Health acting chief medical officer Stewart Jessamine said that, after a few mild winters, the flu season was back to its average, or slightly above average, rate.

"Obviously it is possible the season has yet to peak, although the rate of growth in cases did ease somewhat in the last week. Weekly monitoring means we can soon pick up any change in the situation."

ESR virologist Sue Huang said she believed the season would peak in the next few weeks, and would probably be similar to the 2012 season. At the moment, the B strain was more prevalent in the South Island, while the A(H3N2) strain, associated with higher hospitalisation rates, was more common in North Island.

ADVICE TO PARENTS, SCHOOLS, AND WORKPLACES:

* Flu symptoms include a fever, sore chest, cough, severe exhaustion, and aches and pains.

* Children or staff who are sick with flu-like symptoms should stay at home, including avoiding social functions or sports events, ideally for 48 hours after the symptoms have ceased.

* When coughing and sneezing, use a tissue and throw it into the bin straight away, rather than letting it fester in your pocket.

* Your hands have touched that tissue too, so wash them regularly, for at least 20 seconds, drying thoroughly.

* Viruses can hang out on surfaces for 48 hours, waiting to transfer from a door handle or a desk to to their next host. So wipe down everything your infectious hands have touched.

* They don't always work, but flu jabs are the best defence against the virus. This year more than 1.2 million Kiwis has been immunised and free vaccines have been extended until the end of August for eligible groups. These include pregnant women, asthma sufferers, those aged 65 and older, people with a serious medical conditions, and children under 5 with a history of respiratory illness.

FLU DEATHS:

* There are about 400 "flu-associated" deaths in New Zealand a year, according to a University of Otago study.

* There is no ongoing count of how many people actually die of flu each year, partly because it is difficult to measure. A bout of the flu can often trigger other fatal complications, such as pneumonia, or prove deadly for people already battling another disease.

* Auckland and Middlemore Hospital participate in a flu surveillance programme called Shivers, and recorded two deaths in which flu could have been a contributing factor so far this year.

* Most district health boards contacted for this story had no recorded flu deaths this year.