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The evolving threat of influenza

The flu season has been particularly bad this year, but the way we record deaths may be masking the true impact of the virus. 

“Discontent” doesn’t tell the half of it. This has been the winter of pounding headaches, aching limbs, exfoliated throats and darkened rooms.

Although some people will not notice their encounter with the flu virus – about a third who are infected never get sick at all, although they can still pass it on to others – others, including those who shrug off their symptoms as “just the flu”, will feel the whole potentially fatal brunt of the virus.

“I can’t talk, I’m full of flu,” texted a normally fit and energetic North Auckland woman to a friend early last month, to postpone a chat on the phone. The next day, she was diagnosed with pneumonia and put into an induced coma for 10 days in her local hospital. She appeared to be recovering, but a day after coming off life-support, she was flown by helicopter to Auckland City Hospital and given life-saving heart-valve repair surgery. Before her confirmed case of flu, she had no heart problems.

Michael Baker. Photo/Supplied

Fast and furious

Research by University of Otago, Wellington, professor Michael Baker and Dr Trang Khieu has found that influenza is probably New Zealand’s deadliest infectious disease. More than 200,000 New Zealanders contract the flu each year. Of these, it’s estimated that 400-500 people will die either directly or indirectly from its effects. In the key 65-79-year age group, men are twice as likely to die from the flu as women, and Māori are 3.6 times more likely to die than those of other ethnicities. Those living in the most deprived 20% of neighbourhoods are 1.8 times as likely to die compared with those living in the wealthiest areas.

With still another month or so to go, this year’s flu season came in fast and furious. In some parts of the country, GPs and emergency departments started seeing patients with flu or flu-like symptoms in late March and early April, about two months earlier than in most winters. May saw a steep increase. June, said Canterbury District Health Board (CDHB) chief executive David Meates, was “a June like no other”.

By then, more than half of all flu-like illnesses tested by GPs and hospitals were found to be influenza-positive. According to the Institute of Environmental Science and Research, it was one of the highest positivity rates for this period in recent years.

Trang Khieu. Photo/Supplied

In just one week, the CDHB saw a doubling of diagnosed influenza cases, from 74 to 146. Over the month of June, 908 bed days were due to influenza and bed occupancy rates were “off the charts”. By the end of the month, the number of flu cases was the highest the Canterbury health system had seen since 2009. There were 648 influenza-related hospitalisations. Of these, says CDHB medical officer of health Ramon Pink, 11 people, all with pre-existing conditions, had died of flu-related complications.

The same month, in the Nelson-Marlborough region, hospital wards were running at 105% to 110% occupancy. Schools were reporting a third of their students absent with flu. As in Canterbury, things have calmed down, says Nelson Marlborough DHB chief medical officer Nick Baker, “but it has been a bad season. Last season (2018) was late and light – we watched flu and spring racing against each other. The season change won in the end, but influenza lingered over the summer months in ways that were not typical. So, as soon as we went back into winter, it was ready to strike. A lot of our vulnerable people who weren’t immunised went down with it.”

In one week in June, the number of Aucklanders going to the doctor with flu-like symptoms was 171 per 100,000 people, nearly four times the national average for the same week in previous years. On June 2, 20-year-old Zae Wallace, a promising rugby league player, was the third person in the region to die from a flu-related illness.

David Meates. Photo/Supplied

These tragedies, as well as the early start to the Ministry of Health vaccine campaign and Australia’s woeful winter (more than 300 flu-related deaths have been confirmed across the country, three times as many as in the whole of last year’s flu season), all helped to push up demand for the flu jab.

Pharmac director of operations Lisa Williams says the total anticipated supply of this year’s flu vaccine, as decided last November, was 1.355 million doses. “The actual volume of influenza vaccine brought to New Zealand by the Pharmac contracted supplier in 2019 was 1.1 million doses.” But instead of the usual plateau in late May, demand continued to grow and stockists were warning of dwindling supplies. GPs and pharmacists were asked to prioritise those eligible for publicly funded vaccines – pregnant women, those aged 65 and over, children four years and under with serious respiratory illnesses and people with certain health conditions.

This month, the Ministry of Health acquired an additional 55,000 doses of the influenza vaccine FluQuadri. A further 14,000 doses of Afluria Quad vaccine, originally intended for the private market, were made available to those eligible for publicly funded vaccines.

Overall, says Williams, 1.38 million doses of influenza vaccine will be distributed into the community in 2019. “This is the highest number of influenza vaccine doses distributed in an annual immunisation programme.”

Tragedy:  Zae Wallace was the third person in the Auckland region to die from a flu-related illness this year. Photo/Phototek

Evolving threat

Vaccines tend to have about 50% to 60% effectiveness, but this year’s vaccine, a quadrivalent injection targeting two strains of influenza type A (H1N1 and H3N2) and two B viruses, does seem to be a good fit. However, choosing which strains to target is no easy task. Twice a year, in February/March for the Northern Hemisphere and September/October for the Southern, the World Health Organisation (WHO) amasses data from a growing armoury of global surveillance, virus analysis and antigenic mapping techniques to decide which viruses should be included in the seasonal vaccines for that year.

“But the problem with vaccine-strain selection is the time it takes to manufacture a vaccine – between 5-6 months,” says virologist Lance Jennings. By the time the vaccine is distributed and gets into people’s arms, the circulating virus may have already evolved through a process called antigenic drift, in which slight mutations in the flu-virus proteins allow it to evade the human immune system. “So, you make a decision as to the most likely viruses that are going to be circulating – for us, that decision is made in October each year,” says Jennings. “That virus then has a whole Northern Hemisphere winter to circulate, and it does evolve. We are getting better at predicting this, on the basis of what viruses have been circulating previously and whether the general population has an immunity to prominent strains. But often a virus pops up from left field and catches you unaware. We have had two very mild influenza seasons, but working in this field you are always expecting the unexpected. We haven’t had a bad H3N2 year for several years, but this year is a bad year and continues to be.”

Lisa Williams. Photo/Supplied

The killer in our midst

Understanding just how bad is a further hurdle in our ongoing fight against the virus. Influenza can increase the risk of complications such as pneumonia or respiratory failure, but it has also been found to have a role in strokes and heart attacks. A report, published in the New England Journal of Medicine last year, identified 364 hospitalisations for acute heart attacks occurring within a year before and a year after a positive test result for influenza.

“The main process causing the damage is inflammation,” says Michael Baker. “It is inflammation that makes platelets more sticky, for example, or your heart might be pumping a bit higher and faster because you have a fever. Your body cannot cope with the additional stress of that infection and you die prematurely, whereas you might have been able to carry on for many more winters.”

Many regions are reporting mainly single-figure mortality rates from this year’s flu season, but only a small proportion (an estimated one in 23) of deaths caused directly or indirectly by the flu virus are recognised and recorded on death certificates. Michael Baker puts the blame on our system of recording mortalities. These tend to prioritise one cause of death. If there is an underlying condition that is fatally aggravated by the virus – and once you get to 65, says Baker, half the population has an underlying condition of some sort – it is that condition, rather than flu, that is recorded.

“So, the underlying cause of death might be coronary disease or prostate cancer, but if we had stopped the influenza circulating you might have had another five years.”

With another month of winter to go, and the usual tail of spring-time respiratory illnesses to contend with, data is already being collected to devise a vaccine to limit the effect of next year’s flu strains.

“Can we predict next year? Unfortunately not,” says Nick Baker. “In broad terms, to get two really bad seasons back to back is less common but not impossible. Flu evolves from year to year – if we have the same strains next year, we’ll probably get a milder season. If something new crops up in this Northern Hemisphere winter, then we’ll be at the mercy of whatever new bug comes south.”

Nick Baker. Photo/Supplied

The great pandemic

The influenza virus can never be taken lightly, as history has proven.

In November 1918, Maurice O’Callaghan, a St John ambulance man, attended a call-out to a home in the central Auckland suburb of Grey Lynn. Inside, he found a man lying in bed. He’d been dead for three days. O’Callaghan would tell a government commission the next year that the man’s wife was lying in the same bed, “not dead but driven out of her mind by the fact that she was lying in bed with a dead husband and could not get up”. The man in the Grey Lynn house was one of the early victims of the Spanish flu, a vicious pandemic that would kill thousands of New Zealanders and tens of millions worldwide, beginning just as World War I was drawing to an end.

Anthony Burgess describes in his autobiography how his father came home to Manchester on military furlough in 1919 to find the novelist’s mother and sister dead in bed from the flu, while the young Anthony lay chuckling in his cot in the same room. This was proof, Burgess said, of a god: “Only a supreme being could contrive so brilliant an afterpiece to four years of unprecedented suffering and devastation.”

Viennese painter Egon Schiele wrote to his mother in October 1918 that his pregnant wife, Edith, had the flu, which developed into pneumonia. “The illness is exceptionally severe and critical; I am preparing myself for the worst.” She and their unborn child died on October 28 and he died three days later.

The 1918-19 Spanish flu killed about 9000 here, including an estimated 2500 Māori, almost 5% of that population.

It remains, says retired history professor Geoffrey Rice, “New Zealand’s worst natural disaster, both in terms of mortality and the extent of disruption to everyday life. No event has killed so many New Zealanders in so short a space of time.”

This article was first published in the August 3, 2019 issue of the New Zealand Listener.