When New Zealand's worst public health disaster swept through the country 100 years ago, killing thousands, many people wondered why we hadn't simply closed our borders with a strict quarantine, like Australia did.

The influenza pandemic of 1918-19 is estimated to have killed more than 50 million people worldwide. The death toll among New Zealanders was around 9000 - nearly half the total number of Kiwi soldiers killed in the four years of World War I.

The worst weeks of the disaster in New Zealand coincided with the end of the war in November 1918.

The first outbreak, of what is now thought to mark the start of the later worldwide epidemic, was reported in the state of Kansas in the United States in January and February 1918.

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In New Zealand, the Government was criticised for not quarantining the passenger ship Niagara when it arrived in Auckland from overseas in October 1918 carrying Prime Minister William Massey and his deputy Joseph Ward - and a number of flu cases.

Those cases, however, probably had the milder version of the virus which had caused the first wave of the pandemic, writes historian Dr Geoff Rice in his new book, Black Flu 1918.

The deadlier second wave had already been seeded in Auckland - ready for delivery around the country by railways and coastal shipping - by soldiers on returning troopships.

But despite the Government's unwillingness to impose travel restrictions, the town of Coromandel decided to give it a go.

Public notice of the influenza travel restrictions imposed at Coromandel were published in the Thames Star in November 1918. Source: National Library
Public notice of the influenza travel restrictions imposed at Coromandel were published in the Thames Star in November 1918. Source: National Library

From late October, passengers arriving from Auckland by sea were quarantined for 24 hours and required to pass medical examinations before being allowed ashore through a formalin inhalation chamber on the wharf.

"All roads leading to the town were barricaded and travellers had likewise to go through formalin chambers," according to a 1983 article in the NZ Medical Journal.

The author cites a 1919 journal article, "How Coromandel kept the influenza epidemic at bay," by the town's health officer at the time of the pandemic, Major J. Lovell Gregg.

Rice and health-researcher colleagues, writing in the journal in 2005, said the town remained free of infection and only four people of European ethnicity died in Coromandel County. The county's flu death rate was just 1.8 per 1000 people, far lower than the 5.1 per 1000 for the rest of the Thames-Bay of Plenty district.

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The county's lower death rate was "suggestive of a beneficial impact" from the travel controls.

Professor Nick Wilson, of Otago University at Wellington, told the Herald the 1918 pandemic's rapid spread was probably due mainly to massive troop movements around the world.

"Nevertheless, there is no doubt that travel restrictions helped in some cases in 1918."

In Western Samoa, where the border was open, 20 per cent of the population died. American Samoa refused entry to ships and no one died.

Australia strictly quarantined passengers and crew on arriving ships and It avoided the severe, second wave of the pandemic. The country was affected by the third, milder wave and its mainland pandemic death rate was about one-third of the rate in New Zealand.

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Wilson said that in the next influenza pandemic, even with rapid travel on jet planes, border closure for islands like New Zealand "may make sense in such situations if it can be done in time.

"But unless the Government passes the enabling laws and does simulation exercises to sort out feasibility issues of border closure in advance, this option will possibly not be viable."

Meanwhile New Zealanders eligible for state-funded influenza vaccination will be able to receive their 2018 shots from early to mid-March. For the first time, the vaccines funded by Pharmac will be those designed to induce immunity against four strains of the flu, up from three.