Worldwide, the 1918 influenza epidemic – wrongly called ‘Spanish’ flu – lasted about two years. However, it lasted about six weeks in New Zealand (remembered as ‘Black November’, because the dead turned a purplish-black). It is thought about 7000 Pakeha died and 2,500 Maori. The population mortality rate was about 0.65 percent for the former and 4.9 percent for the latter – eight times as high. (The Western Samoan rate was 22 percent. No, that is not a misprint – more than one in five.) That would be about 35,000 New Zealanders today. It is thought there were more deaths for the whole world from the flu than from the Great War.

This is not the same as the mortality rate for the epidemic, because we do not know how many got the flu. The rates varied quite a lot by region – by a factor of three in the larger towns – which suggests that there were substantial variations among those who actually experienced the flu.

Typically, influenza epidemics kill the very young and the frail elderly; the expected pattern for Covid-19 is it will impact most on the elderly. But in the 1918 case, young adults in the 25-to-45 age range took a big hit. The most likely explanation is an overreaction of healthy immunological systems. (I cannot help noticing that Pakeha male deaths were about double female ones but there was not the same Maori differential; given their different smoking patterns – female Pakeha then hardly smoked – one wonders if smokers’ lungs were compromised.)

My main sources are the work of Geoffrey Rice, emeritus professor of history at the University of Canterbury. The second edition of his seminal Black November is available as an eBook and his That Terrible Time, with its eyewitness accounts, has a useful 20-page introduction.

The cheerful news is that Rice’s work has been involved in our pandemic strategy. He gave a paper to a recent Public Health Summer School at Wellington’s School of Medicine and his research precipitated further work by people who are now at the forefront of dealing with Covid-19.

Are we not lucky that the team is led by Director General of Health, Ashley Bloomfield, a public health physician rather than a generic manager? When the full story is told we will be surprised at just how much preparatory work has been done, and is being done under the radar. For instance, there is a 200-odd page New Zealand Influenza Pandemic Plan: A framework for action (2ed), which includes a list of useful legislation and regulations. (I came across it on the same day that National promised to reduce regulations and wondered whether the party was quite in touch with the pandemic raging around us.)

Yes, historical research has increased our capacity to deal with new issues. I went to Black November because I was interested in the impact of a pandemic on the economy. Alas it was not a lot of help. The economic data are deeply problematic, the world economy was recovering from the Great War and the main pandemic disruption here was less than two months.

I also looked at the 2009 (swine) flu epidemic which lasted about 20 months throughout the world. (The Wikipedia accounts – global and New Zealand – are not nearly as well written as Rice’s.) Its mortality rate was only a hundredth of its 1918 predecessor; New Zealand deaths amounted to 49 – about seven weeks’ road toll.

Covid-19 is thought to be somewhat more lethal than the 2009 influenza. It is too early to make authoritative estimates but death rates closer to the 1918 pandemic are mentioned. The outcome will depend on how well the pandemic is managed.

We are uncertain how the pandemic will sequence, even in New Zealand. One possibility, based on historical experience, is as follows.

The aim has been to keep community transmission at bay, but its emergence is thought to be inevitable – that point may be only weeks away. Eventually the new case rate will peak – probably in two to three months (but don’t trust my judgement). There is likely to be a long tail compounded by overseas outbreaks. Given its nastier characteristics, the 2009 pandemic experience suggests that Covid-19 may be a serious problem here for at least 10 months. Moreover, the measures being taken to reduce the peak, so that the health system can better cope with the extreme cases, may prolong the community transmission phase. I guess things wont really settle down until the world has a proven vaccine which is expected to be at least a year off.

You may be surprised about an economist having to go into this detail – I bet the economic officials have too. But getting a time profile of the disease is critical for thinking about the economic consequences and responses. Given the pandemic detail described here, this topic will have to be covered in the next column.

Note. I am not an expert on pandemics. Although this column has been looked at by some, anything it says should be checked against more authoritative sources.