The report in this issue on the 4th New Zealand Influenza Symposium1 held in Wellington in February this year is a timely reminder of this country’s greatest peacetime disaster and its worst public health crisis. In November various events will mark the centenary of the so-called ‘Spanish’ influenza pandemic, known here as the ‘Black Flu’ of 1918, in which at least 9,000 New Zealanders died in the space of less than two months, mostly from the pneumonic complications of virulent pandemic influenza. This figure is about half the total mortality of New Zealand soldiers in the four years of the First World War, and vastly overshadows the death tolls from more familiar disasters such as the Napier earthquake or the Mt Erebus crash. The best estimates of global mortality from the three waves of the 1918–19 flu are close to 60 million, or three times the estimated total of deaths caused by the First World War.2
Why should we bother to remember something that happened a century ago? Quite apart from the necessity for any civilised society to remember its past, the main reason is that the risk of another influenza pandemic is now greatly enhanced by mass jet travel, as we saw in 1997 and 2009. Some of the lessons from 1918 are still relevant today, and have been incorporated into New Zealand’s current Influenza Pandemic Plan.3 As the philosopher George Santayana famously warned, those who forget the past are condemned to repeat it.
New Zealand was the first country in the world to have its 1918 influenza victims analysed from individual death certificates.4 Death registration was virtually complete for the Pakeha population, but only about two-thirds of Māori flu deaths were registered, some not until the early months of 1919. Recent research on overseas deaths from influenza among the military has raised the Pakeha death toll to 6,671 while the estimated Māori death toll has risen to 2,500. The combined total of 9,171 New Zealand victims yields a death rate of 7.9 per 1,000, which is moderate by world standards. However, this masks the striking difference between Pakeha and Māori death rates: 6.0 per 1,000 for Pakeha and 48.9 per 1,000 for Māori.5
Why did Māori die at eight times the rate of Pakeha in the 1918 flu? There is no simple single answer. The Māori population in 1918 was predominantly rural, and some remote settlements may have missed the protective effect of the mild first wave of the flu in September–October 1918. Yet high death rates were also reported from districts such as South Taranaki where Māori lived in close proximity to their Pakeha neighbours. A variety of factors combined to create a ‘perfect storm’ for a vulnerable population. Poverty, poor nutrition and poor housing were probably contributing factors, but high rates of TB and other respiratory infections, along with widespread tobacco smoking, made Māori highly susceptible to the severe second wave of the 1918 pandemic.6
The impact on the Pakeha population was extremely diverse. Some larger towns and cities such as Nelson, Timaru and Dunedin came through with very low death rates, while smaller towns such as Inglewood, Dannevirke, Taumarunui, Taihape, Invercargill and Nightcaps suffered high death rates. The latter all had high influenza morbidity and a shortage of volunteers to help the sick. Recent work comparing Wellington and Christchurch suggests that differences in response, community organisation, availability of nurses and volunteers, and medical treatment in the temporary hospitals could account for a significant contrast in death rates.7
International research on the virology and epidemiology of the 1918 flu pandemic has grown enormously over the last thirty years, and some of the greatest puzzles about this exceptional event are starting to be solved. Experiments on macaque monkeys with a reconstructed A/H1N1 flu virus have suggested that the 1918 flu was unusually penetrative, bypassing the body’s normal defences to lodge deep in the lungs, causing massive inflammation and severe pneumonic infections.8 Unusual symptoms of the 1918 flu included epistaxis, cyanosis and hair loss. The victims’ bodies were often so deeply cyanosed that they turned black upon death, and rapid decomposition required urgent burial.
The most striking peculiarity of the 1918 pandemic was that it killed mostly young adults in the age-groups between 20 and 45 years. This puzzle has been partly resolved by research on individual death records in North American cities, where two independent teams reached similar conclusions.9,10 They noticed a uniform peak in the age of victims at 28 years. That cohort was born in 1890, in the midst of the world’s previous influenza pandemic, the ‘Russian’ or ‘Asiatic’ flu of 1889–92. The hypothesis is that babies and young children exposed to that virus (probably A/H3N8) suffered damage to their immune systems, so that when as young adults they encountered a different flu virus in 1918 their dysregulated T-cells overreacted and triggered a ‘cytokine storm’. New Zealand data tends to support this hypothesis,11 though recent work on precursor waves suggests a more complex pattern.12
While this is a neat and plausible explanation, it does not answer all of the puzzles about the 1918 flu. Why did Pakeha males in the worst-affected age-groups die at almost double the rate of females, while the Māori age-specific death rates for males and females were almost identical? Why did Japan record a moderate death rate, similar to that of New Zealand, while the rest of Asia recorded some of the worst known death rates?
There is much that we may never know about the 1918 influenza pandemic. Little is known about China, Central Asia and most of Africa for simple lack of evidence, but wherever records have survived and are available for analysis, the death totals continue to go up, as shown by recent work in Mexico, South America and Spain. Optimists doubt that the world will ever see a repeat of the ‘Spanish’ flu pandemic, unless we have a novel avian flu virus unleashed in the midst of another world war.13 However, it is better to be prepared than caught unawares, or as unprepared and complacent as the New Zealand Department of Public Health was in 1918. We may derive some comfort from the news that the Ministry of Health now has stockpiles of antibiotics and anti-viral drugs, along with 20,000 body bags. But we should not forget the salient lesson of the 1918 flu. Hospitals and medical personnel were quickly overwhelmed, and most flu patients were nursed in their own homes. We need better education of the general public in such matters as home nursing, especially of pneumonias, and the revival of neighbourhood support groups. We also need more memorials to remind future generations of how many died in 1918, and more New Zealand history taught in schools to tell them how we coped with the country’s last great pandemic.